Have you wondered?
 

if the space tiles are walkable?
Don't ask me how I got here, I have no clue either. I was just walking and POOF, I was outside on a wall.

Yes they are walkable. They always have been. You can get up there using a jetpack or if you get glitched up there. To get down use jetpack or the 'unstick me' command.

Problem was I never did anything to get up there, I was minding my own business and I was suddenly warped.

Yes, you may sometimes get glitched up there. It's not that big of a deal, just use unstick me if you get stuck.

I assume that those levels use a gmap? Switching levels quickly (usually a gmap and a different level) can cause you to warp to all sorts of funny places, like on Classic, you know the under the bridge glitch max, ;)

Yeah, Ive been there lots of times, Many times from a glitch, and alot of times thanks to the jetpack.

Hmmm....those space tiles really bother me. Stefan really needs to make those space things appear as though they are on a different layer, and scroll at a different speed. It is really rather simple, and it would improve how the game looks enourmously...

Multiple tile layers are planned for the next Graal version, could be interesting to make the stars scroll below the ship yes :)

Well, maybe give it the effect that it would like as though the dropship is flying. That would be neat :) (sort of like what soul-blade suggested).