gulp: gulp.watch(...) not working on Windows

gulp.watch doesn’t seem to work for me, and I think it’s a Windows-related issue. If I use the example gulpfile.js from the readme, create the directory structure (client/js, client/img, build/js, build/img), and a dummy js file in the client/js folder, the gulp scripts task runs normally and minifies the script, but gulp watch fails to update the minified file when the original changes. The console output:

>gulp watch
[gulp] Using file C:\Users\JP\Documents\gulptest\gulpfile.js
[gulp] Working directory changed to C:\Users\JP\Documents\gulptest
[gulp] Running 'watch'...
[gulp] Finished 'watch' in 17 ms

There is no prompt afterwards, it continues “running”, but it doesn’t do anything.