I entered my course schedule for this semester in Evolution at the beginning of the semester. Back then I didn't really remember when was the semester supposed to end, so I set everything to recur every week, forever. A few days ago, however, I tried to change the recurrence from 'forever' to 'until' <some date> in one of the recent occurrences, and selected to apply it to all other occurrences when the dialogue asked me. The results were catastrophic: the recurrence  lasted until a completely different date, and while trying to fix everything I ended up with my calendar FUBAR.

This is not the first time I experience this bug, but this time it resulted in a rather awful data loss...