So, it would seem like there is a bug with the latest version of Twistpad (1.60), that at least for me makes it very annoying to use in certain cases. As such I would really appreciate it if you could release a hotfix for this, and not make us wait until the next usual update is released..Please? :)
Anyway, here's a proper way to duplicate my problem.
Step 1: Create a new file and use tab or some spaces to indent (doesn't matter which). Then just type something on this line, then repeat for the next few lines. Here's what I used:
http://www.thesecondscreen.com/uploads/pre-undo.txt
Step 2: Now, place the marker at the begining of the text on either line and press [ENTER]. You will notice that you got a linebreak as expected. Now try to use the undo function (doesn't matter if you use the keyboard shortcut or the menu). You should now notice that instead of just reverting your changes, it unindents your line!
Here's the result I get after placing my cursor at the beginning of the text on line 2, pressing enter, then using undo:
http://www.thesecondscreen.com/uploads/post-undo.txt
Need more details, just ask :)
EDIT: Linked text documents, as this forum doesn't appear to allow CODE tags to be used.