Weird shipping calculation

[TraceyHand]

I have my shipping set up pretty simply.
£1 per item up to a max of £3 for standard delivery
£1 extra up to a max of £4 for "priority" handling etc (so £2 for 1 item, £3 for 2 items)

It's always worked fine. I have it set by weight and everything in the store has a default weight of 1kg.

However, I've had an order come in today and it's been worked out wrongly online

I've attached a screen grab of the shipping tab. This is exactly how it's downloaded. 2 items, with "priority" option...should be £3 and it's "calculated" £3..but has charged £4.

Could it a some sort of bug where the customer has placed additional items in the cart, had the shipping calculated and then gone back and removed items prior to checking out and Actinic hasn't recalculated shipping?

I can't quite understand why it's done what it's done? anyone come across this before

V8.5.1, btw and first time I've had this issue since upgrading.

[TraceyHand]

ok...think I've worked out what it is
I have my site default weight as 1kg so I don't have to enter weights into all my products.
Since changing from total quantity to total weight, I've not added much stock (been upgrading) but I did today.
I added an item, in 2 sizes with component, attribute and 2 choices..set up with associated products..and set to "sum of component prices"
I forgot, however, to manually set the weight of the MAIN product to ZERO...and it was counting it twice (which I'm sure it shouldn't do, but I knew it did. I just forgot)

anyway, is sorted now...panic over (am surprised none of my customers have mentioned it!)