it's not really a bug, since downgrading isn't supported at all by the packages - as michael said before. The only reason for this function in synaptic is to fix your system in some rare cases.
Generally manually updating libc is a bad idea. Just recompile the package for your distriubtion. -- Difficulty downgrading packages with dependencies https://launchpad.net/bugs/15019 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
