This is a sweet lesson for all the lovers of the undocumented functions. On odd occasion yours truly is guilty of being lazy and choosing a shortcut worthy spießrutenlaufen. From time to time those fits of laziness come back hard.

For a long time I’ve been using SaveAsCompleted internal function on a command bar for custom activities. For whatever reason the function is no longer present in CRM 2015 Update 1.1 and above. My short-term fix? Bury myself even deeper in the undocumented internal land:

if(typeof(SaveAsCompleted) == "function")
   SaveAsCompleted();
else if(typeof(Mscrm.CommandBarActions.saveAsCompleted) 
        == "function")
   Mscrm.CommandBarActions.saveAsCompleted();
else {
   // do whatever had to be done in a first place
}

Lesson: if you are going to use internal functions, at least do it defensively.