checkout bugs, steps 'not found'

Hi,

I am having a couple issues with shopping cart and checkout in (I believe) a fairy simple configuration of HikaShop. I got this installed in the past week or so and have just about wrapped up setting the site up, but I would like to resolve these issues.

Here is my checkout flow:
cart_coupon,login,payment_shipping,address,confirm_cart_coupon_status_fields,end

There are two scenarios in which I sporadically get a "404-not found" error. I am trying to find the exact steps to reproduce and will post when I do.

404 Scenario 1: I have it configured so when a product is added, the popup dialogue 'continue shopping or proceed to checkout displays'. Sometimes when I click 'add to cart' for a product, this pops up, but its a 404-not found. This is sporadic -has this been seen before?

404 Scenario 2: When I am checking out, sometimes it skips the payment_shipping section which I would not expect it to -it then later asks me to go back and fill in shipping if I try to confirm.
checkout->Auto select default shipping and payment methods --- set to no
checkout->Auto submit shipping and payment methods selection --- set to no
I am configured to 'display checkout progress bar without end'. It seems to be that in this case when some steps are skipped, I cannot click on the progress bar steps to advance to them -when I do, I sometimes get a 404 error.

Nicolas -if you need to see the site, please PM or email me. Thanks for all your assistance!

Version: You have the latest stable version : 1.4.8

By the way, I just submitted your contact form with instructions on accessing the site in case you need to (it's not public yet). Thanks!