Copying a page with related child records leads to duplicates of each children
When a page that contains several IRRE children gets copied, currenty to following happens:
- copy record of table "pages"
- copy each record with the pid of the source page to the new page (also all IRRE children)
- when an IRRE parent get copied, this calls recursively the copying of its children
Thus, the IRRE children get copied twice - by their parent record and by the page.
(issue imported from #M5718)