I cannot consistently reproduce this, but I've seen it happen multiple times now. I will mention the common factors between cases where I've noticed this to occur, in case it helps.
Upon resizing the level's horizontal size, via typing the number into the input box, sometimes, the actual on-screen display of the level will be drawn as if the level was slightly narrower than it actually is - I'd estimate about 8px on each side (left and right) is cut off. Vertical size is not affected. Anything that causes the level image to be redrawn again (modifying, zooming) will fix this.
EDIT: On further observation, I have noticed that while sometimes it's both sides, sometimes it's only one side or the other. It always seems to be 8px-ish, though (same amount every time, I think, just not sure if it is exactly 8px). EDIT: And to clarify, I'm meaning 8px of level pixels, not screen pixels.
This is a purely visual glitch; the level's data is indeed the correct size.
Other things that may be relevant:
- This is happening in the current stable release version of the editor, not a built-from-source copy.
- In all cases where this has occurred, no pieces have existed completely outside the new boundaries.
- This has occurred both in cases where the screen start would be outside the new boundaries, and where it would be inside it.
- I haven't seen it occur when resizing via clicking the increase / decrease arrow buttons next to the input; only when typing directly.
- I haven't done any vertical resizing since noticing this bug, so cannot say for sure if it can happen vertically too or not.
EDIT: I have now seen this occur upon loading a level, too.