Yeah, the Quark doesn't have a brake in reverse. So, if you are moving in reverse and then throttle to brake, the controller will simply go forward without stopping. A little hard on the drivetrain.
However, there is a setting that does help a little - I think it's adding some drag brake, but don't hold me to that.
@Jhautz: I wonder when LMT started putting a 4mm shaft on the 1940's. According to the
LMT site, the 1940 and below have 3017mm axle diameter, while the 1950 has a 5mm axle (I apparently was mistaken before about the 1950).