This is a bug that hasn't been taken care for a long time... It seems that the the set area for where mouse cursor changes over the enlarged tile tends to overwrite the mouse area of the program itself, leaving a small area of the program that is accessible. It's random, but the only way to fix this is to quit the program and restart it. I know you've probably got another report like this, but just think of this as a reminder.
Tile Editor Mouse Bug [approx. b12 - 887]
...Huh?
Could I have a screenshot or a diagram?
I think I know what he's referring to, and I confirm this.
Seemingly with a probability of about 0.01% or less, when editing a tile, the mouse gets "stuck" inside the tile editor box. You can still move it around but it won't let the mouse cursor leave that area.
Tell me if this is the bug you are referring to (this may not be how you caused it, but the results should be the same):
Go to the tile editor. Start drawing (holding down the left mouse button). While drawing, hit the Escape key. Nothing happens until you let go of the mouse button. When you do, it goes back to the tile selector screen. Hit Escape again. The mouse should now only work in the area previously defined by the zoomed tile window.
To fix this without exiting the program, go back into the tile editor and start drawing on a tile. Let go of the mouse button and, just to be safe, move the mouse button outside of the zoomed tile window. Hit Escape to go back to the tile selector. Hit Escape again to go back to the main editor screen. The mouse should be fixed.
If this is the problem, then I know what's causing it and will work on fixing it later.