There is an issue related to busybox and some commands being installed twice because of this. I noticed this first when trying to use blkid in a script. Sometimes things worked, sometimes they didn't Later i noticed that blkid can be found both in /sbin/ and /usr/sbin. Depending on some pattern either the one or the other blkid-command was run.
The same i just noticed with "su". Sometimes the command hangs. I solved this for now by adding an alias to my .bashrc and .bash_profile:
alias su="/bin/su"