I've only been doing daycare for about 2.5 years, but I have found that it did take me a while to warm up to most of the parents, espeically in the begining, I was constantly worried they didnt think I was taking good care of their kids or that their kids werent happy, little comments I'd always get concerned about. One mom called me after 2 weeks of care, her daughter had pink eye, where could she have gotten pink eye from, was I allowing daycare kids to come to my daycare with pink eye? etc... my nose was really out of joint with that, but if I had terminated based on that, I'd be missing out, they have turned out to be one of my favorite families! I'll bet it goes the same was as a parent, it takes them a bit to get comfortable with us especically if its their first in daycare hence the awkward comments.
I too have witnessed the massive change in personalities of some of the kids the second their parents open the door. Quite amazing to watch if you ask me!! Good as gold all day long, but miserable, cranky, rude, and uncooperative as soon as mom walks through the door... all for attention....