I've had this issue too. I bulldozed the lot with the school on it in Sunset Valley (got fed up with the town being deserted Mon-Fri) and it left a gaping hole where you could see the sea if you looked closely enough. Moar excellent EA borkage going on there.
I wouldn't say it's sea, it appears to be a missing texture though I'm not certain.
Nope never for me, I tried bulldozing the entire neighborhood the other day (didn't touch the community lots or rabitholes) and I was fine, everything looked as it did before and had no corrupting. Are you using the retail or one of the leaks?
I'm running the razor release which technically is retail.
I'm running the retail version.
I did a test tonight, bulldozing community and residential lots both in Sunset Valley and Riverview. Residential lots bulldoze fine, but all community lots leave blue gaps.
It was residential lots that were turning blue for me. I bulldozed the crappy 'park' in between the Landgrabb and Alto's place and it didn't turn blue. It appears to happen entirely at random. It's story progression in graphic corruption form!