All warranties that you've done it on are void. That's for sure. Products wont have their warranties if you're mixing different products even from the same manufacturer.
And when you do mix the products, it'd be smart to at least tell the customer so that they know their warranties are void. And I doubt you'd want to do that.
Been thinking about this and I like it less the more I think about it.
For the sake of £10 or whatever the difference is (I respect the fact that in OP's case the shop was a 50 mile round trip etc etc) I just don't think I'd bother.
Start carrying an extra bag of rapid setting flexible adhesive in your van and when you use it, replace it the next time you're near a tile shop.