Since you indicate it worked properly in the past but suddenly getting this problem I would guess you need to trash your preferences and re-build.
You should always test this with the included .cpr DEFAULT.
Close Cubase, save everything inside Cubase 7.5 and move it somewhere else. Then open Cubase, select the .cpr that says “default” created by Steinberg, then let Cubase re-build everything and you should be good to go.
Then you can gradually move the stuff you moved elsewhere back to the Cubase folder, but be careful as something in those folders may be what is causing the problem.
I noticed in Cubase Artist 7.5 that the mixer is in sizeable dialog window. There’s no minimize or maximize buttons but you can resize it. As it can’t be maximized, the bug doesn’t occur, as it only seems to occur when the mixer is maximized.
This means you can with the main project maximized and hit F3 to get the mixer up without issue, which is great if you have only one PC monitor.
However, in Cubase 7.5, the mixer is in a window with maximize button. As such, if you restore the mixer window, the project window also restores.
I’d like to know which preferences setting controls this in the XML setting files.
