verse segments seem to be ignored in PTXprint

Question

I have lines like this in a custom.vrs file:

*REV 21:6,a,b

I have USFM marking like this in Paratext:

\v 6a text text text \v 6b text text text.

and I have a module that calls for references like this:

\sr Revelation 21:1-6a
\ref REV 21:1-6a

However, PTXprint goes ahead and prints the whole chapter, seeming to ignore the segments. Can someone help me understand what I'm missing? I'd rather not print more than required. Thanks, Paul