Create a new text file with the following content (1 line):
(begin-file)
foo
(end-file)

Place the cursor just before the word foo (There are two whitespaces to the left). Press Ctrl+Shift+M. A new line is inserted above (What is this command -- I can't find it in the Customize-menu?).
Now press Ctrl+Z (Undo). The new line is removed, but the indentation is lost. I would expect Ctrl+Z to always revert my changes.

I will look into this, Thanks

André Santos
Carthago Software Support
http://www.carthagosoft.net

The formatting got messed up, when I posted. The single line is indented with two spaces.