I just had for the third time my collections wiped out after adding books (actually, it was my wife's 505 which is worse
). All the books are still there, but the 505 doesn't show any collections being present, just books by date,author,etc.
This is totally random. I can't reproduce it, but like I said, it just happened for the third time, so I thought I'd better report it. Both 505's are used under Linux only, with whatever version of calibre is current.