Example of the bug...
You are neutral civ after researching ethics and have researched up to terraforming tech. You invade Altaria which has a current PQ of 14 i.e. they have built soil enhancement and habitat improvement. You Conquer Altaria now the planets has PQ 17 (17 tiles) when it should have 15.
The bug adds the amount of extra potential tiles the planet could have before terraforming techs were built to its current amount. Instead of the remaining amount of tiles that could be built normally with a terraforming tech (non neutral civ).
In my beta2 game this had the result of creating huge PQ planets.
Lenius.