Sometimes when using Ctrl-V to paste, the text is inserted at some random location in the file. It happens the same when you place the cursor with a mouse click or when you use keyboard. I have experienced this bug in mousepad version included with Xfce 4.2 and beta 2, under Gentoo 2006.0.
No matter how I try, I simply cannot confirm this behavior. Is this continuing to happen for you? Any more information about how to replicate it? What version of Gtk+ are you running?
Gtk handles this and nobody seems to be able to reproduce this. Please reopen if you still have this problem.