Bump...
AGAIN... 5.22pre3 and it's still happening. Come on guys, it's a pretty easy fix.
Pasting my description from above:
If you have a collapsed folder as the last visible track in the mixer, adding a new track by double-clicking the empty MCP space puts the new track in the folder, right after the parent, rather than outside the folder as you might expect. Double-clicking the TCP adds it at the end of the list as usual. Here, have a picture:
