Setting showmodified ::= true causes undo/redo to behave in an unexpected way.
To see this, drop an advmemo on a form. Set showmodified := true and run the program.
TYPE:
a
<enter>
ctrl+z
ctrl+y
ctrl+y
RESULT: It took two ctrl+y to restore the text and the return but it should have only required q ctrl+y.
Repeat this but with showmodified := false and the undo/redo acts as expected (a single ctrl+y restores the text and the return).