Which plugin version are you using ? The current version is 1.5.2.

After you upgraded the plugin please delete the slides and create them again.

Also which Browser do you use ? Have you tried Chrome, firefox or similar ?
The normal video should be reset to time 0 when a slide should start. This is a HTML 5 feature, so maybe
your browser on your screen is not supporting this.

On the lastest plugin we don´t see this Youtube effect.