Less not being processed in alpha grid when CSS aggregation is enabled

(I don't know if this is a problem of Omega or Less module, so feel free to move this issue)

Trying to use alpha grid CSS files with Less failed when CSS aggregation is enabled.

To reproduce:

1. Download and install Less 7.x-2.5, lessphp 0.3.4-2 and Omega 3.1.

2. Create a Omega subtheme.

3. Rename the themename-alpha-default.css to themename-alpha-default.css.less and clear the cache.

4. Put the following content at the file:

@color: red;

body {
  background: @color;
}

Expected behavior: You should see the page with the red background whenever the CSS aggregation is enabled of not.
Actual behavior: You only see the red background when CSS aggregation is disabled. If it's enabled, the less code is not processed.

The attached file contains a complete Drupal installation (SQLite db included) where you can see the bug. The root user/password is admin/less-omega-bug.