Completely misread that. My apologies. I am having trouble with an RB751U-2HnD device running 6.11 with an external MC7700 Sierra Card. Connects just fine with the information above - trouble is, always asserts itself as the default route, despite “add default route” not being checked off. I tried via the CLI as well as the GUI and same issue. Does not honour the distance metric either 
I sent an email to support - but haven’t heard back.