Patches to module components are not reported on Available Updates page

Just noticed that if a patch is applied to a module component (e.g. "modules/media_wysiwyg" which is included in the "media" module), it doesn't detect the patch on the "Available updates" page. I've tried placing the patch in the root of the directory and also inside the "media_wysiwyg" directory but in either case the patch is not detected.