https://bugs.freedesktop.org/show_bug.cgi?id=76082
--- Comment #6 from Ilia Mirkin imirkin@alum.mit.edu --- And steam probably uses LD_LIBRARY_PATH. According to http://blog.tremily.us/posts/rpath/, the rpath actually comes first. So my change should probably be reverted, since it disallows using LD_LIBRARY_PATH.
Can you see if starting steam with STEAM_RUNTIME=0 fixes things for you?