Here's an Undo bug in current CVS: Open a new document. Insert an Algorithm float. Write some text. Press <home><Enter> to open a new paragraph above the text. Change the paragraph style to Caption, but don't write anything. Press <down>. ---> the caption paragraph disappears Undo. ---> the algorithm float is killed, though the caption paragraph reappears (labeled "Senseless" because it is).
I did a similar operation in a larger document, resulting in LyX shutting down with an emergency save. However, the emergency save contained only the content of the float, not the whole document -- major data loss. I can provide that document if needed. Regards, Eran