Metamodeling in Hi(OWL 2 QL) and OWL 2 Full

I am reading about metamodeling in ontologies and I do not quite understand what makes metamodeling undecidable in OWL 2 Full and what makes metamodeling decidable in Hi(OWL 2 QL). One point could be OWL 2 Full does not impose strict type separation but isn't it something needed for metamodeling? if it is something not needed then how metamodeling works in Hi(OWL 2 QL) with strict separation type? It would be great if someone pinpoint the cause of (un)decidability in both languages. Thankyou in advance.