Due to the reliance on a check within the pageManager for duplicate page titles (instead of being enforced by the DB) two users can end up concurrently creating a page with the same title.

Both pages will be created in the database although Confluence will only retrieve one of them (by title). The other can be retrieved directly by id. From the user's perspective it will appear that the page they have created has just gone to be replaced by the version created by the other concurrent user.