If you have only a few channels in your main EPG, when you select a channel and 'ok' to go to the single-channel detailed EPG, it will only show the same number of rows as there are channels in the main EPG.

For screenshots, see

http://forum.team-mediaportal.com/mediaportal-1-2-0-rc-547/epg-lines-limited-number-channels-100103/