During scan you're able to select if you want to merge channels or not.
This is needed e.g. for US people which have serveral different TV channels with the same name (like "Sport").
Exporting the channel list is okay.
On import however only the tuningdetails are added completely as the need for a "new" DB channel is determined by it's name and provider.

Read this for further details:
http://forum.team-mediaportal.com/1-0-rc1-svn-builds-271/importing-exported-channel-list-groups-channels-39368/

h4. Steps to Reproduce
1. Scan channels which share the same name
2. Export these
3. Import these

Check the amount of channels exported and present in DB now.