My /usr is a symlink to /data/usr, which normally should work fine. However, glibc installs symlinks to ../../lib64/soname in /usr/lib64 - which doesn't work if /usr isn't in the root.
Workaround is to create a symlink in /data to /lib64 - or to just create new links manually.
Ideally the symlinks installed by glibc should point to the "correct" lib directory - I'm not sure if this is easy to do without breaking something else, so if you can't fix I'll understand...
Don't symlink /usr, it's completely broken idea.
*** This bug has been marked as a duplicate of bug 112413 ***