I disabled the graphics hardware acceleration and it solved my problem. I'm still not 100% satisfied with this solution, because graphic card hardware acceleration is a global OS settings that may benefit other programs, but I have to disable it in order to LabVIEW to work properly.
This behavior appeared after I installed a second graphic adapter into my system (in order to have two monitors, very useful, one to diplay the panel the other the diagram). Maybe if I update each graphic card drivers and install the latest DirectX I may be able to keep the hardware graphic acceleration settings at full.
