The new matplotlib-0.87.5 is in http://gentooscience.org overlay, with useful modifications (this time I removed wxwidgets support). See ChangeLog in overlay.
*** Bug 150342 has been marked as a duplicate of this bug. ***
matplotlib-0.87.7 is out, please add it into portage!
Bumped in portage with minor ebuild tweaks. If there is anything significant in the gentooscience overlay that needs to be integrated file a new bug, at the time I bumped this http://gentooscience.org/ was timing out for me.