It solves few open bugs and most important CVE.
Steps to Reproduce:
1. layman -a x11
2. emerge -v1 =media-libs/mesa-9.1.5
9.1.4 has only just entered the tree.
*** This bug has been marked as a duplicate of bug 472280 ***
Well, 9.1.4 is not stabilized yet and 9.1.5 could be tested directly. This is not duplicate. Maybe it takes more time to stabilize 9.1.5, but this bug should stay open.
Fixed in CVS.