I've been using the google container registry for a few weeks now and there is one thing that is extremely annoying and that I can' get rid of:

I have one docker image which doesn't change at all, except the last layer, a mere 1MB that is updated regularly. When I push this image regularly to dockerhub, as expected, it tells me all layers already exists except the last one.
When I push to google registry, it reuploads everything, just like it was a brand new image.
I would not mind too much if I was not paying for the network traffic, but as I pay + it takes a long time to upload, is that a known bug?