Hi Mike,
I found, even before I went WFP that some new leaded windows were terrible to clean. It seemed that the lead hadn't been treated properly or something, leading to excessive oxidisation. This caused dreadful white streaks and spots which were a nightmare to get off. This would go on for several months, sometimes longer than a year. However eventualy the lead would get pollished with all the buffing and it would stop. I haven't had any like that since I made the switch. But I've been waiting for the first one. My feeling is you may have to do them trad for a while till the buffing effect does its job.
That is of course if that's the problem you're experiencing.
Mark