path mangled in 4.3.9

[Daniel Sproul <sproul+unix@xxxxxxxxxxxxx>]

I am running Mac OS X 10.6.1 and the included zsh (version 4.3.9):

[bebop:~]% zsh --version
zsh 4.3.9 (i386-apple-darwin10.0)

I use .zprofile to set up my PATH, which works fine initially, but if I 
fork another zsh process from inside zsh then my PATH gets reordered:

[bebop:~]% echo $PATH
/Users/sproul/bin:/sw/bin:/sw/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/X11R6/bin
[bebop:~]% zsh
[bebop:~]% echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/Users/sproul/bin:/sw/bin:/sw/sbin:/usr/X11R6/bin

the problem appears to be zsh-specific, given that if I fork a bash 
process my PATH gets properly exported:

[bebop:~]% echo $PATH
/Users/sproul/bin:/sw/bin:/sw/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/X11R6/bin
[bebop:~]% bash
[bash]% echo $PATH
/Users/sproul/bin:/sw/bin:/sw/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/X11R6/bin

The same thing happens to my MANPATH.

I do have the following line in my .zshrc, though commenting it out 
doesn't seem to change anything:
typeset -U PATH MANPATH CDPATH FPATH

any thoughts?

thanks!
- daniel