This seems to be a regular problem with the Bionic. The last OTA update was suppose to address the issue. For me, it only made it happen less often. Motorola says in their site to turnoff the phone and leave it off for a minimum of a minute once per day. I call BS on that one. These phones do not run on Windows!
Anyway, get use to the data connective issues on Droid when moving from WiFi to Cellular Data. I don't recall if I had the problem on my Droid 1 but I have seen the issue on the Droid 3 and the Bionic. Anyone else?