It's not a problem with the neighbourhoods being merged, but with my resetting the sim creation index, which means that unusued instance IDs get "filled in". If you have the full version, your new sims will start being created around instanceID 102. If you downloaded the light version, it will start at 1.
Because J.M. Pescado advices that you don't delete garbage DNA (DNA that doesn't belong to a sim), I didn't do this in any 'hood, although when you merge the game only copies over DNA for the sims it merges in, so the only garbage DNA left over is from Belladonna Cove. This garbage DNA exists for the first few hundred instanceIDs.
When new sims are generated for these instanceIDs, their DNA will overwrite the garbage. However, presumably because the Multi-PT hack doesn't quite work like normal sims, sometimes, the garbage DNA will be left behind instead of the PT's DNA overwriting it. This means that your PT will spawn human babies!
How to fix:
- After putting the Uberhood in your game, load it once with your Multi-PT hack of choice in place. Quit the game without loading any lots.
- Open the 'hood in SimPE. Open the list of Sim Descriptions (SDSC), and sort them by the last column, Instance.
- Scroll down until you find four Unknown instances in a row (this will be a bit harder if you have the light version, since the instances will be mixed in with other Unknowns (these are default game objects such as remote control car). These Unknowns are the links to the PTs.
- Open the Unknown, and then open their DNA (Last tab "More" -> "Open Sim DNA"). If nothing happens, that means there's no DNA, and you don't have to do anything. If you DO get a DNA, you need to select this from the menu, right click and delete it. Save. Do this for each of the PT Unknowns (DO NOT delete the Unknown, only its DNA).
Remember to back up your neighbourhood before fiddling with SimPE.
You can do this even if you have played the uberhood for a while; however, it's important that you do it before any alien babies are spawned, otherwise they may not get alien genetics. The problem doesn't always arise, and I'm not sure whether it only affects aliens with custom skins or regular, default-skin aliens as well. To be on the safe side, you should probably do this either way. If your sim is already pregnant, you can go into SimPE and check the PTs and see if their DNA is alien (their alien DNA only generates once they make a sim pregnant), you can tell by the skintone being a long, complex number (alien/custom skin) instead of a bunch of zeros and just one other number (1, 2, 3 or 4).
Sorry about the inconvenience. :( I had no idea this could happen, and I don't think anyone else did, either (not even MATY). Just ask me if you need any help.