CIRCLE BUG when pushing to gh-pages?

I have a problem to deploy our blog to GitHub Pages by pushing to gh-pages branch.

For example, https://circleci.com/gh/haskell-jp/blog/30 shows CIRCLE BUG just when running deploy script.
As long as I tried, the CIRCLE BUG happened only when the branch matches with the branches specified in the deploy section of our circle.yml.
So I guess the CIRCLE BUG is caused by deploy script.

Here’s our circle.yml, which contains the detailed script.