For aspect ratio (incl. the shortcut keys you can use) perhaps have a look under
(rightclick >) Video > Aspect ratio (& "Keep aspect ratio" just below that).
Maybe also verify setting under
(rightclick >) Options > Preferences > Playlist
Is "Draw subtitles to Overlay surface" selected/checked under
(rightclick >) Options > Preferences > Subtitles [Subtitle properties] ?
P.S.:
Also verify if your graphic-card's settings for 2nd display are correct.