Well, after being away for a year, we landed back in the US on Monday 8th, having complied with the conditions placed on visitors. Anyone that has been following this thread will be aware that last year we applied to extend our stay in the US, which was granted, but we didn't get approval until after we had returned home.
When we got to passport and immigration control, we had a very pleasant discussion with the officer and showed all the relevant paperwork, and have been granted permission to enter for 6 months.
I then asked him about leaving the US near the end of the 6 months and entering Canada, could we re-enter the US without leaving North America.
He wasn't sure so got a senior officer involved.
Their answer was very interesting, if not exactly definitive. They said that their is no hard and fast rule to stop someone coming back into the US, but the decision would be up to the border control officer at that time.
In their opinion, if we had been away for an extended period of around 4 months or more, they personally would not consider us to be "Visa running" and would approve re-entry.
I think the moral is quite simply, tell them the truth, hide nothing and realize that you are a visitor and guest, it's up to you to prove your intentions, not the CBP officers to prove otherwise.
It's nice to be back.