CSS sourcemaps and in-browser Sass editing
It is a bit hard to make the model-based editing (in the Elements panel) play well with source-mapped code, since different users may expect different behaviors (moreover, editing a variable-based property value in SASS may assume editing it directly or editing the variable value instead.) Thus, we have not decided on how this should work, and the CSS-SASS link is just broken at the moment of edit (since the CSS no longer corresponds to the SASS source it was generated from.)
Please star https://code.google.com/p/chromium/issues/detail?id=257778 and leave a comment saying what kind of behavior you expect.