System Information
Operating system: Win10
Graphics card: Geforce 780Ti

Blender Version
Broken: 2.80RC1
Worked: 2.79 and earlier

Can't switch bones by selecting them to draw weight in weight paint mode when a mesh object is selected, which makes the entire purpose of the mode useless, so I have to use vertex groups instead to keep on adjusting the weights. Also can't select any object while pose mode is enabled when working with armature itself, hence it becomes necessary to enable object mode first to proceed, which is mildly annoying.

Have a mesh object selected in weight paint mode. You cannot select bones to which you want to draw the weights, since the armature isn't in pose mode.
Have an armature in pose mode. Try to select another object that's not a set of armature (like the mesh object mentioned above). It won't get selected unless you switch back to object mode on said armature.