Oh, that is interesting. I understand what is happening, though.
You are performing a Sensor Hack, which as a result gives cloaking to all human units.
Cloaked things that produce forcefields normally suppress the forcefield when cloaked, so as to avoid giving away the location. This normally isn't a problem, because only a few units can both be cloaked and produce forcefields (Riot Starships, Champions, etc), and if they shoot (enter combat) they uncloak and the Forcefield comes back.
However, in this case you are granting cloaking to a normal Force Field generator. It can't enter combat, so it can't uncloak until the hack is over.
You seem to have found an odd edge case in the cloaking/Forcefield rules. It isn't a bug, per se, but it probably isn't the way most people would want Forcefield Generators to behave.