now I understand what you are trying to show...
I actually don't experience the same effects like you with mouse over.
Same effect I can reproduce, when I drag slowly Broadcast FM Demod panel,
which on my machine produces more processing which, results in some insufficient bandwidth or clock speed,
while handling the drag and GUI rendering + device sampling.
I would relate this problem to an actual performance of the machine:
Mine is: Core i7 2.5GHz - L3-6MB(I7-4870HQ), 16GB DDR3L .... system bus runs at: 5GT/s
My guess is that your HW performs lower bandwidths in case of Qt/GL event/signals handling,
threfore your HW properties should have been lower than mine, and this effect is already seen with mouse action.
What do you say?