If I want to change the frequency of a clean from 4 to 6 weekly (for instance) the date that it's due doesn't change with two weeks, but it changes with 6 weeks. If you then for instance change it back to 4 weeks, it goes again 4 weeks from the day it said when you selected 6 weekly.
So, I've got a customer who wants to go from 4 weekly to 6 weekly. No problem, the next time it was due is 5 November. But if I select 6 weekly, it's not the 19th, like you would expect, but 17 December!! Maybe it's not a bug, but it's highly recommended to change this. I've only just noticed this, I hope this didn't mess up my schedule, I have no idea how many times I have done that before. Or how much work I have lost because of that.
I've emailed George systems regarding this, hope to get an email back soon.