After several hours of trying to figure out why my stylesheet was no longer updating in live dev, I narrowed it down to an embedded youtube iframe element. When the video is removed and the live session reset, everything works normally again. But when added, css is not updated and the color picker freezes resulting in many of these errors:

Uncaught TypeError: Cannot read property 'styleSheetId' of undefined
Assertion failed: Style Sheet for document not loaded: http://127.0.0.1:49871/main.css

Here is a screenshot of the error link.

The source code I used to find out the problem was simply an html file with an <h1> and <iframe> element and a css file with only one color declaration on the <h1> element. I can provide the full source if necessary.

Brackets version: Sprint 39
OS: Mac 10.9.3 Mavericks
No extensions