I could not reproduce this issue. So few questions :
1. Which Presenter version are you using ?
2. Which video format are you inserting. ?
3. Any particular steps to reproduce. Does this happen evertime you touch the slide manager after inserting sidebar video ?
Adobe Presenter Engineering Team
It ended up working when I was exporting it. If I assign presenters in the pop up window while exporting the presentation then the length of sidebar videos is not effected. If I click on slide manager button in the menu bar and assign presenters to slides there then the sidebar menu videos default to 5 seconds each.
Assigning the presenter frompublish window or the menu bar is the same.
Technically there is no difference.
But it is great that it worked for you.