First of all, regardless if this is a bug or not, I still think this is really cool and should stay in the game! Just update the civic description.

I enacted the "Lifetime Sentence" civic. The description reads, "+1 stability on districts." That effect applied in my games... but it also applied that effect to exploitations as well.

Notice how it says, "+1 stability from Lifetime Sentence on exploitation.

Again, if this is a bug, keep this feature! It's cool! Just change the civic description to read "+1 stability on district, +1 stability on exploitation"