That was fixed in changeset r6445, quite some time ago
(http://trac.edgewall.org/changeset/6445).
They should upgrade their TracMercurial plugin to the latest version for
the Trac 0.10 branch, as they're still using Trac 0.10.4
(http://trac.edgewall.org/browser/sandbox/mercurial-plugin).
-- Christian