In some encounters, boss frames change frequently in unit name, order, hostility - examples are Klaxxi or Protectors encounters in Siege of Orgrimmar. Information that is then incorrect includes raid icons, which complicates the Klaxxi encounter ;)

The default UI additionally reacts to UNIT_TARGETABLE_CHANGED to update the boss frames (see http://wow.go-hero.net/framexml/17688/TargetFrame.lua#1124).

You mean like 4549995?

I assume this is already solved through the commit linked above. Re-open if that's not the case. :)