I have been noticing this same thing....since the update. In fact, I stopped at my Verizon store two days ago to ask about it but we couldn't duplicate the problem. It seems to be random. The reps hadn't heard of this problem before.
In general my experience with this phone and the 2.2 update have been positive, and it's really only a minor nuisance. I've learned to just wait a second before saying hello.