Thanks, it seems like playing with the heirarchy did the trick.
Can you think of any alternative way to detect when a platform object hits a solid? putting a detector on the bottom for each enemy seems redundant, and making an event that says "when <enemey> hits solid - set animation" doesn't work for some reason, until the sprite changes angle, then it's triggered. it's probably a bug.
Nope, not a bug. It's an "undocumented feature."
The reason plaform movement doesn't trigger "On collision" events is because they never actually collide as far as your event sheet is concerned. All the platform calculations take place in between cycles (after the end of your event sheet, and before the beginning). So all the pushing out of solids and such has already happened whenever your "On collision" event rolls around. Sucks, I know. As a general rule I always use "Is overlapping" rather than "On collision."
So yes, even though it's redundant, you should make detectors for your enemies if you want them to have detailed interaction with the environment. A foot detector for contacting the floor, side detectors for walls, etc. You can make it easier on yourself by setting them up in Containers. Click here to read my description of Containers (and be sure to read Ashley's response too, it's important).
Wait... what? It only happens after your sprite changes angles? I'm going to need more details on that, you've confused me now.