Interested to know why you don't consider Bhutans to be appropriate for UK walking?
Indeed, and I'd be interested to know why someone would question someone else's preferences. Except in demanding conditions, I always choose lightweight shoes over boots while my wife almost always chooses boots. My feet can get uncomfortably hot in all but cold weather while hers don't get hot even in summer - we're all different!
Anyway, back to the topic...
I'm not sure about design faults, but I've found that manufacturing faults have worked in my favour more than once. I don't mind them at all!
For example, I returned two pairs of Salomon boots, four months apart, before adding about £20 to the second refund and getting (excellent) Scarpa boots instead. So, in effect, I had the Salomons for 8 months free of charge - not bad for the occasional discomfort of having soggy feet.
More recently, the soles of my Merrell shoes (the best walking shoes I'd ever owned) had worn almost flat. I was still deciding on a replacement when I noticed that the upper on one shoe had started to part company with the sole. So I tentatively asked in Cotswold Outdoor if the shoes were so worn out that fair wear and tear applied or not (which I was expecting). They gave me a full refund that I put towards a more expensive pair of Merrells. Again, months of use for free!