homebrew - Running “brew install moreutils --without-parallels” fails

I’ve recently upgraded to macOS High Sierra. I’ve updated and upgraded homebrew. I’ve done:

brew install parallel

And now I need to:

brew install moreutils --without-parallel

This fails. Looking at:

$HOME/Library/Logs/Homebrew/moreutils/05.make

I can see that this is related to docbook-xsl:

xsltproc --param man.authors.section.enabled 0 /usr/local/opt/docbook-xsl/docbook-xsl/manpages/docbook.xsl ifdata.docbook
error : Operation in progress
http://www.oasis-open.org/docbook/xml/4.4/dbpoolx.mod:3729: warning: failed to load external entity "http://www.oasis-open.org/docbook/xml/4.4/calstblx.dtd"
%tablemodel;
            ^
Entity: line 1:
 %tablemodel;
             ^
error : Operation in progress
error : http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd:155: warning: Operation in progress
failed to load external entity "http://www.oasis-open.org/docbook/xml/4.4/dbhierx.mod"
http://www.oasis-open.org/docbook/xml/4.4/dbpoolx.mod:3729: warning: failed to load external entity "http://www.oasis-open.org/docbook/xml/4.4/calstblx.dtd"
%tablemodel;
            ^
Entity: line 1:
 %tablemodel;
             ^
%dbhier;
        ^
Entity: line 1:
 %dbhier;
         ^
error : Operation in progress
http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd:155: warning: failed to load external entity "http://www.oasis-open.org/docbook/xml/4.4/dbhierx.mod"
%dbhier;
        ^
Entity: line 1:
 %dbhier;

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