Changing my MTU?

Yesterday I upgraded from 5.0 U2 to 5.5.  Everything went fine to the best of my knowledge.  When I got into the office today I logged in to the console and had a bunch of Alerts, which then cleared themselves a few seconds later.  I am sitting here watching the console and it seems like every thirty seconds or so I get anywhere from 2 to 15 VPG0004 alerts, and then they clear themselves up.  The KB for that alert tells me that there are three possible causes for this, one of them being my MTU size.  I tested it at 1500 and I did get the “fragmented” message.  I also get the “fragmented” message at 1490 and 1480, but 1470 seems good.

We are using a 10Gb dark fiber link between our datacenters, and we have jumbo frames turned on.  I never experienced this with 5.0 U2, and nothing has changed in the environment other than upgrading to 5.5 yesterday.  Is this a known issue with the new version?