Thanks for the investigations! Could you tell me the seed you used to make that map? There should be a file named something like "1246215089.map" -- the seed is the number in that name.
Accessibility is one of the Hard Problems that Jetblade has to handle, and obviously it's not perfect yet. Ideally the program should be able to know, accurately, if a passage is passable (and if one-way, that it is one-way). Unfortunately, examining the map to discover accessibility problems is incredibly hard, since you basically have to simulate the physics involved. It's a mess. I've settled for just plonking down platforms wherever I suspect there might be an issue, but finding a balance between "these platforms let you access everything" and "my god, the map is full of platforms" is an ongoing process.
I don't consider having to crawl to be a big issue; after all, crawling was added in part to make the accessibility problem more tractable. It'd be nice if the platforming started out easy and got harder as time goes on, but that's a low priority. The only major problems are when things actually
aren't accessible, either outright or in the "this passage is one-way" sense, since those can break the game.
As for the physics glitch, I'll take a look. You are of course welcome to investigate it yourself; the code's in the TerrestrialObject class.
For those wanting to know when there'll be a playable version: it'll be a long while yet. Keep an eye on this thread, though, because it'll be announced here when it is ready.