Thanks for your question. Attaching a Media Library item to a post/page is a very old part of WordPress, going back to the 2.x versions in 2008-2009. The basic idea is explained here:
Using Image and File Attachments – Attachment to a Post
You can see there that the only time WordPress “un-attaches” an item is when the parent post/page is deleted. You don’t say how you “remove an image from a page” but I assume it is some form of deleting an item block or other insertion in the post/page content.
Attached items do not have to explicitly appear in the post/page content. Part of the original WordPress implementation was the [gallery] shortcode, which displays the attached images. I would guess that’s why WordPress never added any automatic detaching features.
MLA provides UI elements for attaching and detaching Media Library items and some attaching tools in the “Attach Media Library items” section of the MLA Insert Fixit example plugin. It does not have any logic to detect and detach items as they are removed from a post/page.
You can use the “Where-used Reporting” features in the Settings/Media Library Assistant General tab to find “orphans”, items that are not used in a post/page, to facilitate your cleanup tasks. If you do use them, consider disabling them after you have finished because they require a lot of database work to do their analysis.
The bottom line is that detaching items is a manual admin task in the current WordPress and MLA versions. I am marking this topic resolved, but please update it if you have problems or further questions regarding the above suggestions. Thanks for your interest in the plugin.
