Patrick Zaw – Blog

Just like the title says, if you’ve set AllowUnsafeUpdates = true, after a BreakRoleInheritance (on any SP object ie. SPWeb, SPList, SPListItem) AllowUnsafeUpdates will reset back to false.   If you need it to remain true make sure to set it back to true right after you call BreakRoleInheritance:

SPListItem li = list.Items[0];
SPContext.Current.Web.AllowUnsafeUpdates = true;
li.BreakRoleInheritance(false);
SPContext.Current.Web.AllowUnsafeUpdates = true;
li.Update();