Create button not available for users which only have edit rights on a subtree in the wiki (and not on the whole wiki)

To reproduce:

• remove edit rights from XWiki.XWikiAllGroup on a wiki
• create a user
• give edit right to this user on the Sandbox subtree (page and children)
• login with the new user
• go to Sandbox.WebHome

Expected result:

• the user should see the Create button in the Page content menu, so that he can create pages in the subtree, where he has the rights

Actual result:

• the user does not see the Create button in the page content menu, he cannot create a new page other than by creating a link to that page in the content of an existing page and then clicking on this link