This one's a bugger, if you've never had this bug then I guess you don't need this. But if you're hella frustrated with it then heres a kind of fix.

What is it?
For whatever scientific reason MMF2 will swap one graphic for another. This appears to spread over object types, in the aboves case it's swapping out a background object on a layer higher to the sprite with a random frame from said sprite.

I've had this! Enough, tell me how to fix it!
It's a simple fix, but I've only got a method for those making multi-frame games.

Rather than have the game go from-
Level/Frame 1 > Level/Frame 2
You'll be needing to send the game to an intermediate frame that contains no objects. So...
Level/Frame 1 > Clear frame > Level/Frame 2

In my project I've got it set to run a little fastloop to clear some sound channels too. It's easy enough to add in, so have some psuedo-MMF2 code!

Level/Frame 1... Start of frame+global value=0; set global value to frame number+jump to clear frame.

Start of frame+global value>0; set global value to 0.

Clear frame... Jump to frame: global value.

And that kills the bug! Ever since I added this I've not had the repeating graphic bug.