There are several parts of the SWTOR UI that seem to bug out from time to time. One instance is when you zone into a Warzone or Flashpoint the health of your party members does not update so it looks like they are constantly at full health. The second bug is your guild list isn’t updating properly. You might have ten guild mates on at the same time but when you go to the roster you won’t see anyone on the list. There also seems to be an odd bug when your mouse isn’t registering clicks properly.
There is a simple fix for this: hit CRTL-U twice to refresh your UI and everything will be back to normal.