According to the ATLAS web site, the last stable version is 3.6.0, but the ebuilds for 3.7.11 are marked as stable. If the developers mark a build as unstable, shouldn't Gentoo?
Quoting that link: "if Gimp decides to release an unstable/development series marked as 1.3.0, then these ebuilds should be put in package.mask because the software itself is of development quality and is not recommended by the developers for distribution."
So this should be masked.
Well no, it shouldn't. Feel free to file a bug if you have some problem, if you don't, then there's no point in filing bugs.