MASTER_SITE_BACKUP with ${MASTER_SITES:S/%SUBDIR%/${MASTER_SITE_SUBDIR}/}
at the end and MASTER_SITE_OVERRIDE ?= ${MASTER_SITE_BACKUP} are used
together in /etc/make.conf.
So, use simple workaround: replace ( and ) by their URL-encoded %-codes.
(There is the bug in that area still remains, but not fatal:
the combination above don't understand properly ending :tags sometimes
and tries mass fetching with ending :tags unstripped.
Someone should look at that whole bsd.ports.mk/bsd.sites.mk mess)
While I am here, slightly rearrange ending :tags.
4da8d0e6e0