The problem is, one of the buildings is never given back, while others are. This is confusing me greatly. Anyone know what might be causing it?
The attached map has ALL of the spawn related triggers in players 4 & 6.
None.
ForTheSwarm

Ultraviolet -- Yeah he's talked about a lot of that stuff in his casts before. It seems plausible. Especially knowing how Blizzard of yesteryear operated.
NudeRaider -- to clarify: couldn't recall the behavior for every single Protoss building but I was aware the disparity exists.
NudeRaider -- Contained nothing new for me. Didn't know all building's behavior, but very much all unit's. Also Terran balance whine - also nothing new 
Oh_Man -- artosis dropped pretty interesting vid: https://youtu.be/EqZHB8Blra4
NudeRaider -- Ultraviolet
RIVE,
NudeRaider