There is really not too much to explain here! Basically, it's an irritating bug because when you press space or pause the preview it skips some seconds... I hate this bug because when you're trying to pause the timeline to a precise moment so you can cut the clip, it gets messed up! This bug started happening when I updated to this version! Hope you fix it soon :)
Oh and also, I just realized, the timeline stops 2/3 seconds before the end of the video! I think these two things are related because the timeline is actually not in sync with the actual render preview!
Please, could you give more information about your context, because I cannot reproduce your problem. UbuntuStudio 17.04 amd64. Kdenlive 16.12.3 melt 6.4.1 Videos tried: old .avi from mini-DV camcorder (720x576 25fps, 30MB/s) and .MP4 from GoPro (1920x1080 25fps, 15MB/s) Project settings: SD/DVD Wide screen, Frame Rate: 25, no Thumbnails. Play/Pause with Space tested in Project Monitor and in Clip Monitor, and it works fine for me. Is your video played smoothly before stopping?
I'm in kdenlive 17.04.1 and the bug is fixed... When you paused the preview of kdenlive's video the video would just skip a few frames and then stop... the preview was always smooth before... In this new version it's fixed though
Thanks for the update; closing.