I'm not sure about that, but I'll tell you what's happened around here when the RAID fills up completely :) When live filesystem space and snapshot space are full, and 'df' is reading 200%, one of our toasters just crashed. The OS just halted with an error message on the LCD.
Do you remember what the error message was? Filers shouldn't just *stop* if the file system fills up; that sounds like a bug.