I don't think there is a way to stop it playing on into the next folder.
I hope they don't do anything to stop it, either. I actually like the way it does that. Only one of my other daps does that. This little DAP would quickly lose favor with me if it stopped doing it.
It is interesting that you find this behaviour a feature. I suppose I could think of some situations when it might be useful, but playing a complete album from start to end is a very common scenario for me, which is difficult to do with this player. If it was possible to play an album in the correct order through the Music icon then perhaps continuing on to the next folder would be more acceptable when playing through the Folder icon.
An option to play songs from the current folder only would be best. You could turn it off and I could turn it on
This could be an overall option or it could be included in the "Play from..." menu item with a "this folder" option, for instance.
Incidentally, right now the "Play from..." option is a bit messed up when playing by folder. It seems to migrate from the navigation style used by the Folder icon to that of the main database you get from the Music icon, e.g.
1. I select a folder and start playing tracks
2. If I short click "Vol" I can see the list of tracks in the folder, correctly ordered (I can then click the right arrows and "Now Playing" to get back to the normal playing screen).
3. If I click "M" and select "Play From..." I get the options of all songs, this artist, this album or this genre.
4. If I select "this album" it seems to pick up the album contents from the main Music database and not from the Folder list. I can see this is the case if I go back to the main playing screen and click "Vol" and now I see that the tracks are no longer ordered correctly as was the case in step 2, above, but are now ordered "randomly" as if I had got to this track via the Music icon.