If you are on a layer that isn't 'All' or '0' when objects get added in, then the editor layer property of those objects don't apply and it goes straight to whatever layer you are currently viewing. However if you are on 'All' or '0' then nothing is affected and everything is placed on the properly assigned layers.
I tested this, it happens very consistently and the result is the same after disabling all my other mods.
I'm 99.99% sure this isn't a bad G.js implementation issue but it would be funny if it was, even funnier if its a robtop issue