So I have my mouse sensivity set on the same DPI as always, and it's working as it should be everywhere else but not in Warframe after using Alt+Tab in Fullscreen mode. When I switch to for example Borderless Fullscreen or use Alt+Enter on Fullscreen to exit that mode it goes back to normal. But as soon as I turn back to Fullscreen the sensivity gets broken again. The only option to fix it is to quit the game and restart it. I think this started after Rising Tide update. I'm often using Alt+Tab but I didn't have any problems with it after The Old Blood update.
On the video I recorded I'm in the mission with Fullscreen mode and as you can see the mouse sensivity is crazy. After I use Alt+Enter(changing to Windowed) the sensivity goes back to normal.
