Hello Sir, I checked with our Engineer who has more than 20 years in this glass making. He told me that it might be caused by the air compressor, the glass bottle shaping need to be air blowed. But the blowed air are full of dirty water and oil residue which come from air compressor and the operators didn't notice it. As you know, the water and oil is not clean and full of substance. You cannot see it after the high temperature. But you can see it after filled with liquor because the invisible substance is chemically reaction with Acholoh. It is not the whole bottle has this problem, it might be a few of of them are water or oil mixture polluted. You cannot wash it away thoroughly, it only happens after you fill liqour. The white mark is probably the inculstation scale with oil mixture Hopefully my reply will be helpful.
Thanks
Paul