Posted the following in the bug thread, but it seems to have been missed. I'm also not sure what exactly the problem is, so maybe it's worth the thread so someone can try to figure it out:
While Deepening was still in effect I invaded Khazad and used Snowfall in conquering a couple cities, then built Temples of the Hand fairly immediately. After Deepening/Snowfall had worn off, quite a few of the plots around those cities became grassland/plains.
All of the cities pictured have Temple of the Hand.
While Deepening was still in effect I invaded Khazad and used Snowfall in conquering a couple cities, then built Temples of the Hand fairly immediately. After Deepening/Snowfall had worn off, quite a few of the plots around those cities became grassland/plains.

All of the cities pictured have Temple of the Hand.