Gravity directions

[mopa42]

After clicking the random mission button a bunch recently, I noticed something weird.
I've seen code maps with gravity in these directions:

Gravity Direction	Example Code (medium size and complexity)
Up	3114
Down	apple where we
Left	not box ground
Right	birthday not door
None	of ring blue
Down-Left	as up ground
Up-Left	help hill help
Down-Right	and find box

but never any maps with gravity in the Up-Right direction.
Has anyone else seen one? Maybe the random map generator just hates me.
Is this behavior real / intentional / a bug?