install_mu leaves files and working directories in /tmp. The files and directories could cause /tmp to become full, potentially leading to system problems. Files and directories left in /tmp are of the form install* and SUNW*.
Workaround: After install_mu has completed execution, check /tmp for files and directories named install* and SUNW*. If the files were created recently by root, remove them. Or, if the MU was applied to a stand alone machine or server, reboot the system.