I've not had a problem setting a custom screen shot directory / folder & it work, until this build. Though in the past, I've substituted mplayer2 for mplayer. Doubt that mattered for this. I'm now using the portable versions 8.2.4791 - tried both 32 / 64 bit, w/ included mplayer & both had same problem.
Clarify: This v8.2.4791 won't take screens while vid is paused (but all older versions did). It WILL take screens while vid is playing, though that's not much use.
There are 2 entries in smplayer.ini for screenshots.
At beginning of file appears to be default location??: screenshot_directory=.\\screenshots
Note: in one earlier version, the "screenshot_directory=" was blank, & still seemed to take screens fine, w/ a custom location under "screenshot_folder."
After setting custom location for screens in prefs, there's a 2nd entry (along w/ the one above): screenshot_folder=J:\\pics\\Index\\Screens
Slashes & dots are exactly as shown. Seems to be pretty much same as previous versions. Except one older version added 2 back slashes after specified folder: "J:\\....\\Screens\\."
Tried older version still on my PC (that happens to have mplayer2 in it), w/ same custom folder as above - J:\\...\\Screens. The older version (also portable) takes screens fine, during pause.
The setting "use_screenshot" are all =true, in all versions.
Switched out mplayer 0.0.9.0 included in SMP with MPlayer2, dated Jun 5, 2012 from http://mplayer2.srsfckn.biz/ - & it started taking screenshots in pause, as normal. Made no other changes, except pointing SMP to the \mplayer\mplayer2.exe file.