...that it seems odd.
This isn't a bug, per se, but the roof of the subway isn't bound (or whatever the coding term is), so if you activate a spinach, you can leap right through the roof of the subway car and off the screen, just like you can if you're out in the open. While leaping is fun, and while glitchian physics is likely different from ours, it does seem...unnatural to be able to do this. Maybe instead we could...I dunno...ricochet around the subway car like little glitchy superballs?
Or perhaps it's all too much to think about and jumping through the subway car roof is just fine... :)