http://stashbox.org/uploads/11575569...r collapse.png
With the drums track collapsed (it is track 1 and contains 2-6), the skinny little drum items, which are nicely visible, look like they belong to the bass track.
They are below the line separating the selected drum track from the bass track. It looks like the little blank space between the drum track and bass track in the TCP needs the horizontal graphic line as a delimiter just like the channels have.
Hmmm - I just noticed you can select individual drum tracks by clicking in that little blank space, like this
http://stashbox.org/uploads/11575580...ack select.png
or this
https://stash.reaper.fm/oldsb/1157558...ultiselect.png
This means that space is a bunch of little track strips, and only the last track in the folder should have a border, otherwise the blank space would clutter with them.
Cool little feature, by the way. Makes folder tracks a bunch more useful with the mixer pane hidden.