I finally noticed that there were residential lots in Downtown, a factor that I can only put down to deliberate and excessive stupidity on my part with added malicious intent to cause a glitch.
Or is this usual for the NL lots?
I'm not sure what you mean, but there's nothing unusual about residential lots in a Downtown. A Downtown neighborhood is basically no different from a base neighborhood.
Also, as Aspyr has pointed out to me when I e-mailed them, most if not all gameplay glitches are the fault of the original code and have nothing to do with them or the Mac.