Calling theme() within a cached filter breaks hook_custom_theme()

We were getting a Domain Access domain theme error on save, where hook_custom_theme() was being bypassed.

We traced this down to the entity load where the text area was processed and the filter here was calling theme('image_resize_filter_image').

The easy but non-recommended solution would be to make the filter non-caching, but that would have massive negative consequences on sites running this filter. The best option that I could think of was to making the theme callback optional, directly invoking theme_image_resize_filter_image() using a system variable.

To disable the theme() callback, apply the patch and run the following code on your site once.

variable_set('image_resize_filter_theme_image', 0);