mailing lists showing in AD

[clareq]

Since moving all our mail boxes to 365, and shutting off our on prem Exchange, we've noticed that any mailing list created by staff is being written back into AD as, for example, Group_0385bd87-4c46-40d9-8dd2-7dc05a2b6e7a. The description tells us the name of the Mailing List and it also exists under groups in Office 365. How do I stop this from writing back - it's making AD look untidy!