Oh, I just describe that I found this problem happened at what time (maybe have other time).
However, I try to explain your questions:
you mentioned when alarm (pop-up) window visible , however i never see the alarm pop-up becoming visible.
My mean is, in past days, when alarm window correctly pop-up, e.g. the alarm of first-time.

you also mentioned that the user must set the task as "Completed" once again . this is where you lost me.
look following describe and image:

# when alarm window pop-up


# set "Completed"


# alarm window disappear, but the item on To-Do list not has change.


# so, I must set "Completed" 'once again' to change it become next.


what tag should i look at in the default.ics file (assuming that this is the correct file) to see if the alarm is reset correctly. for example, the alarm that should have pooped up at 1PM today is a recurring task for the 7th of each month.
.....
and after i do a "Complete" on it by right-clicking on the task what should the new value be?
the correct ICS will be like:(for 2012-10-07, important part only)

COMPLETED:20120907T180000Z
X-RAINLENDAR-LASTALARMACK:20120907T182838Z

and if you do a "Completed", the new value should be:

COMPLETED:20121007T180000Z
X-RAINLENDAR-LASTALARMACK:20121007T183818Z

Explain:
COMPLETED: Last "Completed" time. will affect the display on the to-do list.
X-RAINLENDAR-LASTALARMACK: Last alarm marked time. will affect the time that next alarm is triggered

thanks for the additional explanation.

however, in your example you showed an alarm window that has popped up and how you have to do the "Completed" action twice. it appears that you are able to do this because the alarm window did pop up. keep in mind that i can not do this "Completed" action twice since i never see the alarm popping up for recurring alarms. when i do click on "Completed" (without ever seeing the alarm popup) the task does get removed from the task list.

i am not sure what release you are testing with or what release your test alarm was added with. this may have something to do with this bug.

keep in mind that when i say that the alarm never pops up for recurring alarms i am referring to alarms that most likely were added before the bug that crept that was eventually fixed in beta 112. i do not know if this plays a part in it, that is, it was an existing alarm (whose alarm date/time might have gotten messed up due to this bug) rather than a brand new test alarm.

what shows up in the ICS file for my example of an alarm (recurring) that should have popped up on 10/7/12 at 1PM before i click on "Completed" is:

COMPLETED:20120907T170000Z
X-RAINLENDAR-LASTALARMACK:20121007T170000Z

however, what shows up after i clicked on "Completed" is:

COMPLETED:20121007T170000Z
X-RAINLENDAR-LASTALARMACK:20121107T180000Z

while the COMPLETED date is correct, the LASTALARMACK date is wrong from what you said it should be. for both the before and after values listed above the date is one month more than what you indicated it should be.

here is the complete section for this task (i'm assuming that the task blocks go from a BEGIN:VTODO to an END:VTODO) after i did the "Completed" on it:

BEGIN:VTODO
DTSTAMP:20101128T001658Z
STATUS:COMPLETED
UID:{150cf248-1daa-7142-9ec6-614784ed4fc8}
SUMMARY:Check thermostat for low battery
CATEGORIES:Chores
CLASS:PRIVATE
DUE:20111107T180000Z
RRULE:FREQ=MONTHLY
PRIORITY:0
COMPLETED:20121007T170000Z
X-RAINLENDAR-LASTALARMACK:20121107T180000Z
X-MOZ-LASTACK:20121107T180000Z
LAST-MODIFIED:20121008T141246Z
BEGIN:VALARM
ACTION:AUDIO
TRIGGER;VALUE=DURATION:PT0S
END:VALARM
END:VTODO

i then re-edited the alarm to set a new "Due date" to next month (11/7/2012) to see what happens (do not get confused as the original due date was 11/7/2011):

BEGIN:VTODO
DTSTAMP:20101128T001658Z
STATUS:NEEDS-ACTION
X-RAINLENDAR-LASTALARMACK:20121107T180000Z
X-MOZ-LASTACK:20121107T180000Z
UID:{150cf248-1daa-7142-9ec6-614784ed4fc8}
SUMMARY:Check thermostat for low battery
CATEGORIES:Chores
CLASS:PRIVATE
LAST-MODIFIED:20121008T143547Z
DUE:20121107T180000Z
RRULE:FREQ=MONTHLY
PRIORITY:0
BEGIN:VALARM
ACTION:AUDIO
TRIGGER;VALUE=DURATION:PT0S
X-RAINLENDAR-ALARM-TYPE:alert
END:VALARM
END:VTODO

what is interesting is that the LASTALARMACK date was not changed while the COMPLETE value is no longer present.

according to the previous post:

COMPLETED: Last "Completed" time. will affect the display on the to-do list.
X-RAINLENDAR-LASTALARMACK: Last alarm marked time. will affect the time that next alarm is triggered

i'm guessing that because the LASTALARMACK date is not being reset correctly that that is what is causing the next alarm to not pop up correctly.

does my data and analysis of the problem seem to bear this out?

thanks!

There are two separate issues here. The first one which anoob found is that the COMPLETED date is not set if the task is currently shown in the alarm window. The second is that the ack time for the alarm is always increased from its previous date when the task is completed so if you somehow manage to set it to a future date you will never see the alarm for the task anymore. I'll try to fix the problems in the next build.

rainy,

is there a workaround until you get it fixed?

preferably is there a way to just re-edit the task so that the alarm will pop up? i tried resetting the due date as i explained previously but this not seem to update the tag/values correctly to what 'anoob' said they should be.

if not, can i edit the ICS file manually for my recurring alarms so that they will pop up in the future? and if so what tags should i edit or remove?

one thing i am puzzled about is i that thought that this alarm pop-up issue was fixed in beta 112 yet i am still seeing it. is this because i already had existing alarms?

What I test was when the alarm dialog is shown, checking it as "Completed" doesn't mark it as Completed, instead is more like a Discard. It updates the alarm.ini file with the same values as X-RAINLENDAR-LASTALARMACK and X-MOZ-LASTACK, but not the Completed tag, even if it already exists, not only on new one.
To "update manually" the alarm these 3 values are need to be changed, but the problem still there when the next time the alarm dialog appears.

gwa999, this is my workaround :
# Re-setting due date as the next date that alarm should pop-up.
# Deleted old alarm setting, then re-setting a new alarm.

Jorge_Luis, if "update manually", except need to change these 3 values, also need to clear the alarm.ini content.

one thing i am puzzled about is i that thought that this alarm pop-up issue was fixed in beta 112 it was fixed another alarm pop-up bug.