Isaac, you make a compelling case. I'll undo the edit of subprocess.
Also, I may have found the culprit: iTerm.app. It turns out there is a well documented issue with duplicate PATH variables in OS X 10.10 when using iTerm:
[
github.com]
My symptoms were nearly identical, just with tcsh, not zsh. I had two PATH variables (other duplicates as well) in my tcsh environment but (ba)sh purges duplicates when it inherits them, which eliminated the instance of PATH set by /etc/profile, which was subsequently modified by ~/.tcshrc. The other PATH was just the minimum standard path. Updating my iTerm eliminated the second PATH (and the other dupes).
--iain
