The new path selection in 2.8b 831 is buggy. Double-clicking sometimes selects the entire path, but sometimes the first click selects just a segment and the second click either deselects the shape or changes the selection to the opposite path on a 45° angle. It usually happens when one path is selected and I hold shift and try to select another path. This is not a problem with double clicks not being input fast enough to register as a double-click.
Fixed it. I had tried to implement segment section but the current implementation is not ready, yet.