I have recently encountered a possible bug because when I copied attributes from one clip (Basic Motion & Opacity) and pasted to another which resulted in the aforementioned parts pasted correctly BUT the clip changed to 75% speed instead of the original 100%. Please note speed wasn't selected in the paste attributes box.
Can't say it is a bug, because I have neither had this happen or heard anyone else mention it. I copy paste attributes, particularly basic motion and opacity or filters all the time and from FCP4.5, 5, 5.1, 6 and now 7, I have not seen this happen once.
However, FCP can do screwy things and that usually means time to trash preferences and repair permissions, a common regular maintenance routine that we all do. A search of this forum will reveal methods and software from Digital Rebellion that makes this a simple task.
We Trashed the prefs a week or so ago and I regularly repair permissions. FCP hasn't been right for our system for sometime now can't really put our finger on the problem. We have had some issues with crashes with a BM Decklink Studio card but I wouldn't of thought that could screw with internal workings of FCP??