If (instead of using [+]-key) you depress [5] of numeric keyboard, does that "repair" your problem?
Also deselected "Remember movie window size"?
And "Remember movie settings" (under 'General')?
Any Nvidia drivers updated recently (
attended/unattended) or changed settings? Using Clone mode or
(Depending on version of drivers I think you should be able to select your secondary display as your Full screen device.)