Odd placement of the "Opus" string

[Christopher Culver]

I'm typesetting an orchestral work with 2.8.0 that has two movements,
and so I am using a \book holding two \scores. In the header to \book,
I assigned a value to "opus". However, this opus number is being
typeset down alongside the title to the first movement, instead of up
top with the work title where it belongs. Is there a fix?

I hope this isn't an obvious question, I'm a newbie, but I've tried to
search for a previous answer to this.