Fixed navbar dropdown links won't scroll

[xmf]

If the viewport is smaller than the list of dropdown links of a fixed-top navbar, there is no way to scroll down to view links that are beyond my view. The reason being obviously that the entire navbar is "fixed". I've tried to make .navbar-collapse scrollable but it won't always scroll down to the very end, it's very confusing.

Can be reproduced using your example here: http://getbootstrap.com/examples/navbar-fixed-top/, both on mobile and desktop. I'm using the newest Chrome Browser.

Any thoughts on this are VERY MUCH appreciated - thanks!

[cvrebert]

Duplicate of #12738.