Biowell appears on map for captured city but is not really there

[greggbert]

1) Gain the tech to make biowells.
2) Capture an enemy city with a biowell
3) The BIOWELL appears as a visble improvement on the captured city's tiles but the game ignores it.
4) Move a military unit over the (image of the) biowell and you do not get the option to pillage the biowell
5) Move a worker on the square with a biowell and one of the recommended options is "construct biowell".

Bug or feature?

 

[Xenotitan]

Perhaps it was partway built when you invaded? Is the turns to build it reduced compared to building it elsewhere?