Take any scrollBar ( I tried in HelloWorld, anyway, you need an application, where you will have more than 1 control, to see, where focus is) and click on knob, on left and on right arrows (up\down, if it is vertical). It make some motion (knob moves...) but scrollBar doesn't receive focus. Click in free space between knob and any of two arrows. Some action about knob motion will be done and focus will be received.

It looks like bug.