It seems a fresh compilation of the latest socks5clients (1.0r9) dumps core when runsocks is run. It seems the problem lies with the dynamic loader, and not socks code itself (well at least after stracing it seems so). With various programs the point of error lies at different points, but always during the loading of libraries. runsocks is a simple wrapper which sets LD_PRELOAD and LD_LIBRARY_PATH so that non-socks5-programs (e.g. /usr/bin/telnet) can be socksified. It has it's own dynamic lib which plays a bit with bind(), connect() etc. and I've never had any sort of problem with it before. This problem occured with glibc2.1.1-3 as well as some earlier version. Since I made several upgrades (primarily gnome-oriented) at the same time the problem may lie elsewhere (although strace does lend the idea that it's dieing while loading libraries).
I would guess this is more of a socks5 problem, that assumes that glibc provides and will always a provide a certain interface for internal functionality.