I have clip.mp4 and clip.srt in folder.
When I click on clip.mp4 smplayer starts and video plays with subtitle as should, but when I've trying use default hotkey j (next subtitle) to turn off subtitle it doesn't work.
If i open Subtitles-Primary track I've see that subtitles now playing are not marked with black dot as selected, if i manually click on clip.srt here then subtiltes were marked and hotkey j starts work as it should.
BTW, z and x hotkeys (subtitles delay) doesn't works too, until subtitles are selected.
Version: 19.1.0 (revision 9191) (64-bit)
Using Qt 5.6.0 (compiled with Qt 5.6.0)
Using MPlayer SVN r37955
Windows 7 x64