Comment # 6 on bug 76082 from Ilia Mirkin

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?