I'm using SMPlayer 17.10.0 with MPlayer on Windows 7 (x86). The following problems are a bit hard to describe:
With some (not all) audio MP3s, playback somehow gets truncated if the total duration is not much longer than the content. For example, the playback of an MP3 with an indicated duration of 1 min. 23 sec. may stop prematurely at something like 1 min. 21 sec., cutting off a speaker's last word or the final chord of some music. I thought such MP3s might be faulty, until I noticed that the same files ended properly in Windows Media Player, which also indicated the same total duration.
With MP4 videos, the effect is quite different: a sort of bounce, where the final frame will be repeated, flashed briefly on the screen as the playback stops, with the audio sometimes lingering beyond the video, as well.
Note that in all the situations I'm describing, there is very time left beyond the content. If, on the other hand, the total duration is more than a couple of seconds longer than the actual content, the playback will end correctly.