I'm using [webassets](http://elsdoerfer.name/docs/webassets/index.html) in my Flask application using [Flask-Assets](http://elsdoerfer.name/docs/flask-assets/) and I'm having trouble with the `depends` option when creating [bundles](http://elsdoerfer.name/docs/webassets/bundles.html).

In my case I'm bundling LESS files from the following directory structure:

```
/static
 \_ /css
     \_ /bootstrap
     |   \_ bootstrap.less // This file @imports variables.less and custom.less
     |   \_ variables.less
     \_ custom.less

```

My bundle looks like this:

```
css = Bundle(
    "css/bootstrap/bootstrap.less",
    filters="less, cssmin",
    output="dist/base.css",
    depends="**/*.less"
)

```

With these settings, the LESS files are rebuilt whenever a change is made to either `bootstrap.less` or `custom.less` but NOT `variables.less`.

From what I understand, the expression used for the `depends` option is a [glob](http://docs.python.org/2/library/glob.html) instruction and using the one above should simply go through all directories recursively and pick up any LESS files. However, it never seems to pick up on any changes made to `variables.less`.

In my attempts to fix this, I've tried the following options for `depends`:

* `"*.less"` - Doesn't pick up anything (as it's searching in the root of the project directory, I believe, where there are no LESS files anyway)
* `"**/*.less, myproject/static/css/bootstrap/variables.less"` - Doesn't pick up on any changes in any file at all.
* `"**/*.less, myproject/static/css/bootstrap/variables.less"` - Same as the one above.
* `"myproject/static/css/bootstrap/variables.less"` - Strangely enough, this picks up on changes made to both `variables.less` AND any other LESS files (such as `custom.less`).

In essence, the last item is the "solution" for my problem but I have no idea why it works the way it does, so it doesn't sit well with me. Can anyone provide an explanation or a nudge in the right direction here?

Thanks!