Apartment boiler system. Very hot water coming out of cold water tap
I agree with the other answer about the mixing valve/lack of check valve being the most probable reason. 

However, I just had a first last night (which still has me searching online today, thus landing me here at this page)

I got a call for the same reason. 27 story building. The apartments are split into 2 zones for the plumbing and those zones have several risers for each stack of apartments. We only had this issue on one riser (10 apartments vertically in middle of building). Only these 10 apartments were affected, and it was only the bathrooms.

Most smaller buildings, the cold water is typically higher pressure, but this is opposite due to gravity (boiler room is on roof). After going through all 10 apartments vigorously, we isolated it down to one apartment. The bathroom sink faucet was feeding hot water into the cold line as other tenants on that riser opened up their cold. 

So while a bad mixing valve or check valve issue is the most likely culprit, there is a chance it is one little faucet in the building that is screwing up everyone.