Erg, it's getting pretty complicated to get everything working, heh. Still, try this one: http://dl.dropbox.com/u/15217362/platform-jumpthrufix.zip - is that working for everything now?
I can imagine :P Well I just tried that one. It fixes both of the previous bugs I mentioned, but now there's another new one. When overlapping a platform while standing on top of another platform, the player thinks it's in the air, like so..
<img src="http://dl.dropbox.com/u/17634050/platbug3.png" border="0">
I didn't jump or anything, just walked up to it. I can probably work around this by making the platforms (invisible tiles) 1px thick so the player base doesn't overlap them when standing underneath. Fortunately my character is short enough for this to work. Not sure about the platform enemies though. I'll try that now..