Same problem here for ~ 6 months. The gang at RIM's support forum haven't been able to figure it out. First appeared with my 8830 running 4.2, but interestingly enough, it remained when I gave the Storm a short spin (not for me, thank you). So, I don't think its a device problem, but a BIS problem.
The next phase of this bug is all return characters are stripped from emails sent from the BB; say buh-bye to paragraphs.