I can't reproduce this on Fedora 17 x86_64 (glibc-2.15 + patches). Can you reproduce this with vanilla glibc? Also, can you reproduce this with newer versions of eglibc. glibc-2.15 had ATOMIC_FASTBINS removed, i.e. made into an implicit option, so there's no way to disable it.
I can't reproduce this on Fedora 17 x86_64 (glibc-2.15 + patches). Can you reproduce this with vanilla glibc? Also, can you reproduce this with newer versions of eglibc. glibc-2.15 had ATOMIC_FASTBINS removed, i.e. made into an implicit option, so there's no way to disable it.