
I came across this today. I was adding a mult-level menu for my mobile breakpoints. So I did that to the 480 BP. I then unchecked it from the larger BPs' (768, 980 and 1280). When I came to preview it, the menu icon (hamburger) was huge. The reason (I think) is that it took the size from the default and scaled to that. When I added it to the default size first, it scaled down to the 480 & 320 correctly.
I hope this helps - Pablo will tell us if this is not correct.
Alan