MyVideos loads the entire contents of a folder when entering it (okay).
After you played a video inside that folder, it reloads everything _again_.

On SMB shares with 50+ videos inside one folder, this can cause that MP does not respond to anything for 15 seconds.

Depending on the amount of files in a folder, extrems of several minutes where MP does not respond can be reached.

http://forum.team-mediaportal.com/mediaportal-releases-315/horrible-slow-networkshares-78339/