[TSVN] cannot save in diff program?

 I used to be able to go through the changes between my working file and a
version in the repository and choose to "undo" some of those changes by
right-clicking on each individual line and choosing "use this text"

Now when I attempt to save my changes after doing this I get an empty
"STOP" message box.

Is this a bug, have some settings changed that I need to change back, is
this something that has already been corrected, or is this no longer a
feature of the application?

I am using the release version 1.2.0.3602.