Funny colors in the pathing overlay

I noticed today that the pathing overlay can sometimes show some funny colors, not just the standard green to indicate pathable, red hash for unpathable and low-intensity to show "need to re-explore". In this image, there's also yellow, orange, and purple (though the latter two only have a couple tiles each):

Does anyone know what these colors mean?

Looks like something is leaking through from an alternative debug overlay we have which uses the same backbone.

Huh. That'd make it a bug, wouldn't it? It seems to happen reliably around these stacker towers. Update 4.1 | v0.8.5 (b598).