This is exciting.
I tried some insertions and they went alright. Before I became concerned about my mental health I issued:
1042 AddEntry.sh 29.4. test that succeeded
1044 sudo date 013110002011.23
1045 AddEntry.sh 30.4. test that failed
Here, AddEntry is just a shortcut to "rainlendar2 -a". The date I set is 31.01.2011 around 10 am. And suddenly everything (regarding QuickAdd) went kaboom again.
So this clearly has something to do with January, the last few days of it. Early January things worked alright.
I wish I could deliver better information.