And if I may interject a more fundamental concern - the bugs are intended to be set by the crew to the speeds THEY desire - not to specific speeds drawn from the AFM or other docs. Say you want to 'bug' Vref+5 - because it's SOP, because you have a failure that requires +5, because you like that number. Go ahead, do so. You may in such a case be very unhappy to find your (perhaps carefully chosen) bug shifting around as a result of the INC REF switch. It may also be invalid for it to move.
Suppose (and I'm not directly involved with the Q series, so the exact scenario may not apply, but the concept should) that you have a failure which requires landing with an increased speed. Perhaps a control restriction. In that case the extra speed isn't there for stall margin, it's there to give more control power.
Now I flip the INCR REF switch. Fine, I already have my bug set high. So I quite reasonably leave it alone - the extra speed now does double duty for both control power and stall margin. If I instead double added, I may be over gear speed limits, or tyre limits, or at an unusually nose-low attitude (with risk of nosewheel strike on touchdown, or ...)
My point being, the bugs are to be set by the crew, as an aid to the crew in monitoring speed, with the speed chosen based on all kinds of factors, including simple airmanship.
To devise an automatic resetting of the bugs which would not get someone inadvertently into trouble might be rather hard. And, perversely, as an OEM it's valid to assume that crews have airmanship - or common sense, if you prefer. Once we take the action out of the crew's hands, though, our hardware doesn't have any sense, common or otherwise; we must design it in. And sadly, common sense is sometimes VERY difficult to specify.