viewport at-rule disables Chrome 29 CSS Inpsector

When the @viewport rule is used at the top of your CSS, Chrome’s CSS Inspector stops working and all line numbers are printed out as line 1.

Comment out the @viewport {} rule or move it to the end of your CSS to fix the Inspector.

This error did not occur in Chrome versions previous to 29.0.1547.57

Here’s a JS Fiddle demonstrating the problem.