I never did get my PD8 to view fullscreen after it starting doing the same thing you describe.
I tried remove, re-install PD8. I did not re-install the OS however.
Now I have PD9, so no more problem, Plus I also ungraded Win XP to Win 7 64bit.
Maybe if you contact Cyberlink support.
Carl312: Windows 10 64-bit 8 GB RAM,AMD Phenom II X4 965 3.4 GHz,ATI Radeon HD 5770 1GB,240GB SSD,two 1TB HDs.