[duskwuff]

I suspect a hack was involved -- the animation leading up to the construction of a Zerg Extractor involves the drone hovering over the geyser temporarily. This requires the unit to be put into a "floating" state which wasn't properly cancelled if the build failed -- queueing up additional move commands would then allow it to clip through barriers.

A number of similar bugs with queued commands existed. I get the sense that this feature wasn't adequately tested. :)