@IDont:
Any thoughts on how to proceed with the "TMPDIR" issue?
I have been following the bugreport at busybox.net, and glibc is blamed for for this behaviour. Their only suggestion for a workaround is two busybox binaries. Maybe not the most elegant solution...

Today I adapted a script of mine which needed to ping to check a connection. As I did not want to run it as root, I decided to install Iputils-ping for now, replacing the busybox ping.