Canada Post module giving crazy prices or doubling boxes

Hello,

I have a 1.3.7 Zen Cart with the 1.3.7d Canada Post module. The module works fine most of the time, for most customers, but sometimes it goes crazy.

Let me explain. Most of the time, CP prices are similar or lower than UPS. Sometimes, it gives a price that's way too high on some addresses. Those addresses are "suburban" addresses that CP makes normal delivery to at normal rates. I made sure one of them was valid.

The other problem is with the number of boxes doubling (and the shipping charges too) on some order. This is how this issue goes:

1- Customer puts one item in cart.
1- Customer goes to cart and clicks "checkout".
2- On step 1, CP is selected and indicates "1 box to ship".
3- When customer clicks next, the "step 1" page is showed again, but this time CP module says "2 boxes to ship" and the shipping charges are doubled.

UPS is unaffected.

The crazy thing is that you can go out of the checkout process (by clicking a random menu item) and go back and it might work. I've had occasions where it worked fine, I left the checkout process only to go back to it right away and see this issue again.

I've setup this cart over a years ago, but I don't remember making any modifications to the CP module. The UPS module is the canadian version addon, not the original US that comes with ZenCart.

Any ideas?

Thanks!

Other question, does the 1.3.8 CP module works on a 1.3.7 cart?

Anybody has any ideas for me?