Document isn't saved properly when saving after using the tab's close button

A document isn't saved properly when it is closed tab's close button, and then saved from the dialog that just opened.
Another user doesn't see the changes made, and can edit the same document, which causes the first user's data to be lost.

To reproduce:

• Log in as an admin
• Edit a document (for example the title)
• Click the close button on the tab
• A dialog opens asking you to Save
• Save
• You can check that it is saved by opening the document again
• Leave the browser open for now

• From another browser, log in as an editor
• Open the same document

Expected result: The document has the changes made by the admin user
Actual result: The document has none of the changes

The editor user can now edit the document. By doing this, the admin user's changes are lost.

When this has happened, the admin user gets an exception when trying to edit the same document, stating "Item seems to have been removed externally". See the screenshot. You can get rid of the exception by logging out and in again.