Page move: page selection -> possible to select a sister page

60 r23757

I have a page (A) which has a sub page (B1).
I add a second sub page to A (B2), and choose to move an existing page. I cannot select A, nor one of its parent page, but I can select B1. (i.e. I try to move it at the same place)
I validate, and I have now two subpages, with exactly the same url, but one is marked for delete.