Hi,
That's not a bug.
When you go to your UPS or CanadaPost counter to send a package, if you swap the width, length or height together, the package still has the same dimensions. You're just turning the package on itself, why would the shipping rate change ? I don't see why this would be a bug. It's just how it is supposed to be and HikaShop is indeed ordering the dimensions so that it can group the products in the cart together in the most logical way to improve the shipping rates.
For example, if your selling post card products, regardless of how you enter the dimensions in the different products, the algorithm will automatically stack them together in the package as you would do in real life so that you get the most accurate rates possible.