Hm, I did some more testings but it's not "as expected", but IMHO also not as @Lowlander says there would be no connection.

Example:
- I scan all playlists from my HDD folder.
- They are imported into my "Imported Playlists" folder.
- I put the playlist out of the "Imported Playlist" folder in a self created playlist "folder" (and even rename it)
- I do some changes to my playlist and do a rescan of my HDD playlist folder.

There should be 2 ways to handle this:
1. If it would be a sync like MM does with 'mp3-files MM should see what playlists have newer timestamps and "update" them (or import the new one, so there is a duplicate)
2. If there would be no connection, as @Lowlander says, it should import all playlists again - this would be fine too, so I could once again move the "newer version" from the "Imported Playlist" folder to my self created folder.

But...
none of those 2 options happens. The "changed" playlists is simply not imported again as if it wasn't there anymore.

So there MUST be a connection to the "old import" for it sees "This is the playlist xxx.m3u (though it is moved and renamed) again, so I don't import this, no matter if it has a newer timestamp".

IMHO this makes no sense.
Either MM should do a real "sync" and update / add newer playlists,
or MM should ignore the imports before and simply add ALL playlists to "imported playlists" again...

I have some playlists from other programs that have been imported by MM into the "imported Playlists" folder.

I then did some changes to existing playlists, deleted some playlists, added some playlists and did another scan of my library and saw... nearly no changes to my playlists. The imported playlists weren't changed, the deleted ones weren't deleted, only the new ones Had been imported.

So it seems to me other that the rest of the library where changed mp3 are updated or deleted, there is no real update / sync concerning playlists?

Can I change this behaviour, for I use the playlists to choose the songs I sync with my android device...?

That's correct, once a Playlist is scanned in it's no longer connected to the Playlist file.

My Playlists are created in Foobar 2000 & saved to a Playlist folder on PC - I then import the playlist to mediamonkey via add/rescan files. The Playlist imports correctly to MM as an "imported playlist"

Issue: a subsequent edited Playlist with the same filename as the original will be rejected by MM add/rescan.
i have to delete the original playlist & then rescan the new edited playlist if i want to retain the playlist name.

It appears that MM can detect changes in music files but not playlists. Unlike windows when you try to save an edited file using the original filename it prompts you to accept the change.