Coupons - am I understanding this correctly?

[BooJewels]

One of the things I'd like to be able to do on my newly upgraded CC6 store, is utilise the coupon codes to try and encourage additional related purchases.  I think I understand how this will work, but need someone to check my thinking please.

For example, I have a bracelet for sale at £56 GB pounds and would like to offer a £5 discount if they buy a matching pair of earrings at the same time.  I have 2 pairs of earrings available that match, one at £19 and one at £32.  I put all three items as 'Assigned Products' for the relevant coupon code and if I set a minimum spend at something like £70, then the coupon would allow the discount for the bracelet and either pair of earrings, but not if someone just bought both pairs of earrings (their sub-total = £51).   I'm trying to just create one coupon code that I can publish on all three product pages.

It appears to work when I put things in the basket and start to checkout, but if I remove one of the items, the coupon discount appears to persist with the lower value basket - is there a later point where it realises the coupon is no longer valid and removes the discount?  And will it work as I'm thinking - with discount for 2 products from 3 assigned?

I bought from one of my own suppliers at Christmas that had a free gift for offers over a certain value and when I checked out, one small item had sold out and was removed from my order, yet the coupon for the free gift persisted and my invoice said my order would include it - I didn't get it and queried it with them and they said 'but your order was below the value threshold'.  I was a tad irritated as the lower order wasn't necessarily my fault, it was their stock issue and the paperwork persisted with the free gift included and I wouldn't want my customers to encounter a similar confusion and irritation - why is the coupon discount not removed when one of the qualifying products is and the subsequent order value falls below the threshold?  If you only put one item in, or the two cheaper ones, I does say it doesn't qualify.