Maya Bug - displayColor in maya 2015

Let's call it bug. Before maya 2015 SP5 we used maya 2012 in the studio. I don't know which version is the first where this "feature" was added to maya.
If I run this line it produces RuntimeError:

 cmds.displayColor("headsUpDisplayLabels", 16, dormant = 1)  

The funny thing is it changes the color but produces error. So I can handle it with exception.

 try:  
   cmds.displayColor("headsUpDisplayLabels", 16, dormant = 1)  
 except RuntimeError:  
   pass  

I know what you are thinking: Holy crap!

So is there something I don't know? Or what?