That is correct. When placing MLeader labels for Concept Plants, it is not prompting to place additional leaders lines, and it is also not moving the labels to Paperspace if necessary. I don't see any notes in the code for why it is this way. The code is a little messy in there, so my hunch is that it was just part of getting the MLeaders to work, and some final cleanup of the code never happened.
I'll get this on the calendar to get finished.
In the meantime, you can select the Mleader, Right Click, and choose Add Leader.