This bug happend with the following setting:
Linux Fedora Core 4 / KDE 3.5.3
Rainlendar Version 2.0.2 (b32) Build on Jul 28 2006
I am using three calendars, an event list and a todo list. When I boot up KDE it sometimes happens, that the positions of the windows are randomly switched, meaning that e.g. the events list is in the place of the first month and the first month is in the place of the todo list and vice versa. Which window changes its position with which window seems to be random as well as that this bug happens at all. I am _not_ using dual monitors but I do use eight desktops in KDE.
Apart from this, Rainlendar works great for me under Linux. I love the fact, that I can have one single calendar file for Windows and Linux.