No, nothing that simple. I'm running simple single hood testers - Pleasant View and Strangetown - although they are my genetically editted copies. I will put the standard shipped hoods back in and see if they disapear on me - thankyou for the thought.
update: it's not my modified Neighbourhood bases. It's not merely having apartments in my game nor creating apartments from existing buildings in a hood. It's not moving playables, or even multiple apartments of playables into apartment blocks. In fact it is now nothing that I can reproduce, which is a bitch because I don't know what it was so I don't know what not to do again. At the moment I am leaning towards it being some custom content that I used in making my previous apartment conversions - probably a custom door or window, but I can't prove it and I can't reproduce the problem.