No conflict detected in case of concurrent edit of a document title

Reproduction steps:

• Create a new empty document and save it
• Open the document in edit in two tabs
• In first tab type title "Foo" and click any save button
• In second tab type title "Bar" and click any save button

Expected result:

• A conflict window should appear since the document title changed concurrently

Obtained result:

• The document title is actually erased