The following issues have been addressed in the 4.0.1a minor patch.

• Using a "/cast!<pet ability" command no longer disconnects players.
  
• Mousing over objects that generate a cogwheel should no longer cause the client to freeze or disconnect.
  
• Guild Tabards should no longer display on characters not actually wearing the Guild Tabard.
  
• Floating combat text should always appear.
  
• NPC Health Bars/Nameplates are now appearing correctly.