Tab width varies in PR diff

This has been an issue for awhile, but it used to be the case that highlighting the code would redraw the tabs all at the same width. Highlighting no longer does this and the tab widths remain sporadically different throughout the code.

I'm using Safari 10.0.1. Here's a screenshot of the issue. I highlighted starting from the first character (a space) after the tab on line 187 and ended the highlight to the (including) first tab on the next line (188). I.e. All that's highlighted on line 188 is a single tab character and the first 2 characters on line 187 are a tab and a space and the highlight there includes the space. You can see that the beginning of the highlight and end of the highlight don't line up and reflect the different in the asterisk placement on each of those lines. They should be perfectly aligned as both lines start with <tab><space><asterisk>.