I would initialize your Cubase profile. You can quickly try out, if a clean Cubase profile will solve the problem, just by loading Cubase in save mode.
Here is how it works.
1.
Hold down + + (Windows) or + + (Mac OS X) and start Cubase/Nuendo
Then you’ll be presented with a menu, where you should select “disable program preferences”. The Cubase will boot up “clean”. Then check if you have the same problems.
If everything then works, then you can make it permanent by either - deleting your normal preferences (not backing up… easy and fast to do), or by renaming your old Cubase profile to something different (example: Cubase 7 old). After that start Cubase again, where it will build a new initialized profile automatically. Deleting the profile without backup, can easily be done with the mentioned (1) procedure (delete program preferences).
that was indeed an issue in C7.0.6 but shouldn’t appear in 7.5 anymore. Trashing your preferences should solve the problem for good. Make sure you trash C7 preferences as well, otherwise the problem will reapear.