This has been irritating me for some time. Whilst mapping, I tend to playtest frequently to see how things look in game. However, often after returning to hammer from running TF2, my mouse ceases to use the tool I have selected, and instead serves only to navigate the grids/look around the 3D view. Reloading the map or restarting hammer does not fix the issue, it fixes itself after a few minutes. Could anyone please tell me what is happening or, more importantly, what I can do to fix it?