traktor pros midi controller icon?

ive always kept up with traktor pro updates. i dont remember exactly when but one of the updates not long ago added this to the interface:

looks like a midi controller icon or something. loacted at the top of traktor's interface, in the middle, is the master clock. going to the left, youll see cpu (displaying the load on the processor), audio (displaying audio connectivity) and then this icon.

whats it for? i got a vci100 hooked up. its sending and receiving midi fine. yet that icon isnt illuminated. i think i remember seeing it lit blue before but it aint now... can anyone explain its functionality?

I haven't got Traktor or the manual in front of me but it is explained in the manual addendum.