Getting a strange error using a basic gulp/express build watch.
Directory Layout
project/
- sass/
- style.scss
- gulpfi
I was having the same issue with the gulp-ruby-sass plugin. I found this blog post which explains that there are a couple of bugs in the gulp-ruby-sass plugin regarding source maps. They have both been closed a little over a week ago. If you upgrade to gulp-ruby-sass~1.0.0-alpha this should fix the issues your having with source maps.
If that doesn't work the article I linked to above shows how to use the gulp-sass plugin which which doesn't have the source map issue.