I had this last week,went inside and had on 2 windows out of dozens so not to bad. I must have got lazy and didn't scrub enough and go right up to the top of the panes,you will get this far more if you don't use a stiffer brush. Hot water helps with this problem a lot,like I say I got lazy and had it left on a couple of Georgion windows but without the hot water I would had far more windows left with the same problem.