You're receiving this bug because the package in Summary has produced _FORTIFY_SOURCE related warnings indicating the presence of a sure overflow in a static buffer.
Even though this is not always an indication of a security problem it might even be. So please check this out ASAP.
By the way, _FORTIFY_SOURCE is disabled when you disable optimisation, so don't try finding out the cause using -O0.
Your friendly neighborhood tinderboxer
Created attachment 250261 [details]
+*arb-5.2 (20 Jun 2011)
+ 20 Jun 2011; Justin Lecher <email@example.com> +files/5.1-bfr-overflow.patch,
+ arb-5.1-r1.ebuild, +arb-5.2.ebuild:
+ Version Bump, fix buffer overflow, make gcc46 resistent, fix build failure,