Z/os USS: 'man' fails to read bookmaster

we have two z/OS instances, on one the 'man' command finds input content, formats and displays it and caches the results. All good:

SYS$JB:/VERSYSB/usr/man/C/man1: >man -x date
Trying /usr/man/C/cat1/date.1
Trying /var/man/C/date.1.*
Trying /usr/man/C/man1/*.book
        Trying /usr/man/C/man1/bpxa5mst.book
        Looking for topic "date" in /usr/man/C/man1/bpxa5mst.book
        And converting to codepage 1047
  date -- Display the date and time
...

On the other, it can't find the input content, so for example 'man ls' says it can't find any content for 'ls':

TEST4:/u/test4: >man -x date
Trying /usr/man/C/cat1/date.1
Trying /var/man/C/date.1.*
Trying /usr/man/C/man1/*.book
        Trying /usr/man/C/man1/bpxa5mst.book
        Looking for topic "date" in /usr/man/C/man1/bpxa5mst.book
        And converting to codepage 1047
        Can't read this book. bookread() reported error: 112105
        Trying /usr/man/C/man1/fcxd3m10.book
        Looking for topic "date" in /usr/man/C/man1/fcxd3m10.book
        And converting to codepage 1047
        Can't read this book. bookread() reported error: 112105
...

apparently failing to chew the Bookmaster input. The bpxa5mst.book files on the two systems have the same checksums.

Any ideas ? I'm guessing that there's an issue with Bookmaster config, but I sit on the *IX side of the house so it's just a guess.