Been searching around, found a Work Around this whole mess.
I tried it and it worked.
After you open your map. Go to your task manager and end GameOverlayUI.exe and that should fix it until Valve fixes it.
Jup, working perfectly, it would certainly be better if it was fixed rightaway, but it´s only 4 clicks once you start hammer, shouldn´t be that much of a problem for everyone willing to map
so gogogo!!! just 74 days left
what does it actually do? I dont know if mine is on or off