Sourcegraph CEO here. There are indeed some glitches in syntax highlighting, on other languages as well. I hope it doesn't significantly detract from the product value, but I understand it is not good.

Here's why it's happening:

We're using TextMate syntax bundles, which require the Oniguruma regexp engine, which only has partial pure-JavaScript implementations that can run in the browser. We use https://github.com/bcoe/onigurumajs, which is great. We think something in this stack is producing different results than using C-based Oniguruma, and we'll work on it.

The good news is that we'll open-source whatever improvements we do make, so other folks building web-based syntax highlighting components will benefit.