Yseult hi,
It should not happen, so, perhaps, there is a bug in EventIDE or some problems with an decoder filter. Could you please send me your experiment (via Dropbox), such that I can make a quick test.
If you use videos <1GB with no audio track, I would recommend to play them with the new Video Sequencer element. It does the same job as the Video Player element, but preloads and decodes a video before playback, in advance. Video Sequencer can be much more accurate in frame timing, plus you can set a custom playback speed.
I will update you, if I find any problem with the Video Player element.