ID:2417303
 
Resolved
Expanding the movie size (more frames or more directions) and then undoing while a frame in the expanded area was still selected could result in errors.
BYOND Version:512.1461
Operating System:Windows 7 Pro 64-bit
Web Browser:Chrome 71.0.3578.98
Applies to:Dream Maker
Status: Resolved (512.1462)

This issue has been resolved.
Click to add a new frame, undo it = error
Here is a gif: https://gyazo.com/92096529d26cbbe2000da4d28eb0973c
Lummox JR resolved issue with message:
Expanding the movie size (more frames or more directions) and then undoing while a frame in the expanded area was still selected could result in errors.