Filter logic has been put into the template loader while it not belongs there.

[hakre]

Some time ago, filter logic has been introduced in the template-loader. Looks like a fix for the inability to handle attachments propperly (WP misses more and more a strict request parsing so that newer features tend to introduce more and more bugs).

The code has not been removed yet. It should be removed there or put into a more appropriate location.

The code in question is:

remove_filter('the_content', 'prepend_attachment');

in /wp-inclueds/template-loader.php around line 30.

[hakre]

related: #6357 , code in question was introduced by ryan

[Ninos Ego]

Is it planned to remove this filter in one of the next releases? I think this hack should be removed from code, otherwise you'll see the attachments image on the attachment page if you're using the the_content filter for compiling shortcodes in widgets or somewhere else.
For theme developers it should be very easy to add a new line of code to their single-attachment.php (or use map the attachment image to the post_thumbnail function). If you want I can publish a patch...