Mixture of wieghted + non-weighted items

Joomla 3.1.5 / HikaShop Business: 2.2.1

I set up standard shipping.
I've added weight restriction to it of 100g
If all my products have zero weight then the postage is correctly calulated as 0
If all my products have a weight of 100g+ then postage is correctly calculated as £3.50 + £1 per item
However if I have a mix of zero weighted products and weighted ones, then postage is calculated incorrectly.
i.e. It add's £1 per item for the non-weighted items aswell as those which are weighted.

The only way I could get around this was by adding a customer postage price under each zero weighted product with a value of 0.
Is there a no easier way for this to occur? I thought zero weighted product were meant to be excluded from shipping prices?