Andy:

The only way I've been able to get this to work is through "Fake Sheet Mode".
You said

"In BIAB 2014/381, I go: Lead Sheet -> Opt -> Notation Options -> 'New Line each' and 'part marker' from the dropdown."

- When you get to the Lead Sheet window, click on "Fake Sheet Mode" at the top (perhaps yours is already set to this)

- Then click on Opt. If Fake Sheet Mode has been enabled, the check box for it will be available in the bottom left corner. If it's greyed out, go back to the Lead Sheet window and enable it.

- The way to get the printout to show a new line at every marker, can be controlled by the box that says "Fakesheet bars/line".

- Say you have a 3 bar intro, then a part maker, then a 9 bar verse.
In the bar/line box, type "3,4,5,4" (assuming you want all the other lines to be 4 bars, and omit the quotes)

- Then OK > Print > OK Preview Graphics

- Now the lead sheet should show a new line for each part maker. If not, just keep experimenting with the bars/line numbers until it works.

Good luck!
LLOYD S