Why can't I select bones in weight paint mode? I cannot select bones once in weight paint mode. I have already turned off "Lock object modes" and I can switch between pose mode and weight paint mode so that's not the issue. I can go into pose mode and move my mesh around so I know it's parented and I know it has an armature modifier. I am not sure what I am doing wrong. 
Here is a link to download the file. I am using the latest version of Blender at the time of writing this 2.82

https://mega.nz/#!QUpljRYQ!kFUGNKmHashr6CYRD-hbAy9V3pSqacHfjZB7C1xzXdg
In 2.91 this is no longer working. Selecting a bone in weight paint mode throws both the mesh and the armature into object mode. Then we have to switch back to pose mode in the armature, then back to object mode, then select the mesh, then switch it to weight paint mode.