Just a heads up that I had this problem with my previous phone (Samsung Infuse). I purchased a new phone over one month ago (Droid Razr Maxx HD). I am 99% sure I did *not* have the problem for most of that month. Recently, however, I accepted the offical updgrade to Jelly Bean, and ever since then I am having this problem again
In my research, it seems to be caused by a combination of things: Exchange 2010 (Exchange 2007, 2003, & 2013 don't seem to have this problem), and particular devices and/or device ROM updates. That being said, I haven't been able to pin down the exact cause.
I am considering a hard reset since upgrading to Jelly Bean, but I'd hate to go through all that work & the problem not be solved. Frustrating!!