I would think there's an issue with Navisphere. Did you stop and start your browser ? Try restarting the management server on both SPs. http://  ip>/setup, restart the mgmt server, wait a few minutes until it's available again and do the same on SPB. then enter Navisphere again and see if the T is still there.
Okay,   I thought I knew most of them, but this one has me stumped.  I have a host with the "T" in a circle icon.  Usually when I see that, I know the LUNs are Transitioning.  What does it mean with a host?  Is there a reference to the obscure icon definitions somewhere?  Thanks.
Navisphere Icons