My new game is using the Platform movement object (pmo) because I wanted to have more slopes and valleys, not just straight walkways. It works extremely well, but once I got my game onto an actual device, a problem arose. When I have a layer behind the layer that the player is on (and all the platforms, enemies, etc.) collision doesn't work on objects unless they have "collision with box" checked. Obviously I can't check that on slopes and ramps. So when the player hits them, he just falls through. Deleting the background layer eliminates this problem.
The other issue that I've been having since the beginning, is slowdown when I bring in an extra layer. Having a front layer with the HUD and onscreen buttons that scrolls at 0.000, doesn't seem to cause problems, but putting anything behind the player that scrolls slowly, brings the game down to a crawl (it runs at about 20% speed).
I'd be happy to send anyone the .mfa if it would help.