csh error with "umount -f" and "cd .."

[Kai Fabian <Kai_(_dot_)_Fabian_(_at_)_god_(_dot_)_de>]

Hi, if I work with csh (and only with csh, sh and ksh doesnt have this
problem), mount a drive (e.g. cd-rom), go into this directory, unmounting
this mount with -force and do a "cd ..", then the system stops! mount
/dev/cd0a /mntcd /mntumount -f /mntcd .. CRASH Greetings from Germany 
Kai