Popups do not work after validation of form fails

This seems due to the fact that the js popup files are included in form_alter. This hook is not called when the form is retrieved from cache (for example, forms are cached if there is a ajax file upload widget in the form). Therefore, popups don't work after form validation fails.

To make it work, I defined a custom validation function which includes the necessary files again (basically calling popups_add_popups() and including popups_reference.js).

Oh, and this problem exists with other modules as well (e.g. organic groups, pathauto, etc.) ...