PATH variable case-insensitive?

[Koch <omgoch@xxxxxxxxx>]

Using zsh 5.0.2 (x86_64-pc-linux-gnu) with the following file contents in 
./test.zsh:

PATH=bar
path=omg
echo $PATH

and running zsh ./test.zsh outputs:
omg

Is this a bug? It's certainly not my intention to have this meaning attached to 
this program, since it goes against POSIX.