Has SP2 for AutoCAD2012 been installed?
The AutoCAD2012 SP2 readme file (English) file says the following issue is supposed to be resolved by applying SP2. If you feel the following issue is the same as what you're experiencing, then SP2 should resolve it.
AutoCAD Updates and Service Pack downloads
Service Pack 2
- On a 64bit Operating system with VBA loaded, you may not be able to restore AutoCAD after minimizing it.
* Before installing updates/SP's, I recommend creating a Windows Restore point