If I'm working on a text file and make a major error, asking Tea to Undo either with ctrl-z or Edit->Undo will cause the file to lose all of its text. "Redo" will bring the text back, but only with my mistake still present, and hitting "undo" from there simply blanks the file all over again.
I just installed the latest Tea and verified that the bug is still present by
-- opening Crapbook, which had ~1550 characters in 21 lines
-- Replace All of href~hrefa
-- Edit->Undo (all text vanishes)
-- Edit->Redo (text with mistakes returns)
-- Edit->Undo (text vanishes again)
I noticed the problem when I first installed Tea sometime last year, but only now had time to report it. In case it's helpful info: I'm running 32-bit Linux, kernel 2.6.31-1 which was compiled by the Simply Mepis crew.