Can anyone shed any light as to why Gulp would be taking so long to compile our Compass project?

When we run gulp compass

gulp.task('compass', function() {
    gulp.src('./docroot/sites/all/themes/pmc/sass/*.scss')
        .pipe(compass({
            config_file: './docroot/sites/all/themes/pmc/compass/config.rb',
            css: './docroot/sites/all/themes/pmc/css',
            sass: './docroot/sites/all/themes/pmc/sass'
        }))
        .pipe(gulp.dest('./docroot/sites/all/themes/pmc/css'));
});

we get

[gulp] Starting 'compass'...
[gulp] Finished 'compass' after 4.22 ms

but it actually takes about 1 min 50 to build our stylesheets

Doing a compass compile is actually much quicker.

Now I suspect this is project related as I've used Gulp on other projects and haven't seen the same issue. I wonder if our use of https://github.com/restorando/compass-retinator is causing the performance lag -- even so, a compass compile with this is still fairly speedy.

Any ideas?