`source` seems to break Upterm

This is very strange; when I try to source ~/.profile in Upterm (with zsh), I get this error:

This doesn't appear to be an error from the shell, but from Upterm itself. Sourcing ~/.profile from iTerm or Terminal, of course, works.

So I try source-ing something else, something innocent like .zshrc. That gets even weirder. It appears to exit without errors, but it didn't actually run to completion (I know because I have a fortune | cowsay at the end of my .zshrc which didn't show up), and once it finishes "running", nothing else works. Trying anything results in "Upterm: command * not found":

If I had to guess, it looks like source itself is being overridden by Upterm somehow, and not being implemented properly.

Let me know if you need me to post the ~/.profile or ~/.zshrc files themselves.