When you upgrade, one of the steps is to select your profile. Some people intuitively select 'SDL Trados' (which actually means 'old' Trados, not Studio). Because you do not select your profile every time you create a project (well you do have this field, but it never needs any change so that you hardly notice it), you can easily forget about the choice you've once done. The same reason is why you cannot reset it to default: your shortcuts are already those by default for _this_ profile (SDL Trados = 'old' Trados). All you need is selecting 'Default' profile. If you have other preferences, you can save ['Export user settings' option] your profile having assumed it any other name of your choice (other than Default, SDLX, SDL Trados). In case if the Universe collapses, go to Setup->Manage User Profiles again and select 'Change user profile', then locate what you saved.

The profile has inside:

• Editor settings (like font adaptation, colors and so on - look in File -> Options -> Editor)
• Keyboard shortcuts
• Window settings (like termbase viewer on another screen)

This is what I can confirm from my usage.