Bug - Hanging Gardens Effect does not expire

[Fistleaf]

I captured Moscow with Hanging Gardens and also nearby St Petersburg. When both have grown to the same size, has the same number of military police, 1 temple each, connected to same luxuries, I researched Steam Power.
Even though the Hanging Gardens is supposed to be expired, Moscow still has no unhappy citizen whereas St Petersburg has one unhappy citizen. The city screen still shows 3 content faces beside the Hanging Gardens.

[Gramphos]

How do you know that is has expired?

[Fistleaf]

The discovery of Steam Power supposedly renders the Hanging Gardens obsolete. But till the end of the game, the "3 extra content in the city" effect is still there and I checked the citizens and found that it is effective.

[Gramphos]

Yes, that should stop it. Is it specific to if you capture a wonder, or if you build it yourself as well?

I'll test some things later.