When selecting/cutting/pasting using the editor, I find that occasionally the cursor will be restrained to motion within a few lines on the screen; I can still make changes, but the cursor won't leave this area of the screen. Saving the file clears it right up, though.
More info: You can fix the bug by simply repositioning the cursor with the mouse. Also, the way the cursor is restrained: After you clear the selection, you cannot move the cursor down beyond where the end of the selection used to be until you click below that line with the mouse.
Okay, another update: The bug actually only paralyses a single block, the character either at or just beyond the end of the selection. You can't key the cursor into or over that block until you resave the file (mouse clicking will get you beyond the block, but you still can't cross it with the cursor until you save. I save quite often, so I didn't notice this little caveat). I have a sneaking suspicion that the editor is percieving it as an EOF character, but I really can't say for sure.