Without being able to see the listing in question, I don't think we can give you a very good answer, @fergua3.
I think the GSP is going through a glitchy stage right now. I went onto the UK site to browse some vintage electronic items and found that while the GSP shipping price showed up in "list view," when I actually viewed the listing I got the dreaded "contact seller for shipping options, blah blah blah" message in the shipping section. I had to switch to the .ca site to see the (94 quid!) GSP shipping charge in the listing. Everything seemed fine at Checkout and there were no adjustments to the shipping charge or the import charges.
You say that the import charges show up as a line item, but do they change between the listing page and the Checkout page? I seem to recall a quirk back in the days when we did battle with the US GSP that import charges would shift to the shipping charge if a Best Offer negotiated price dropped into the tax-free limit. I know you said nothing about using Best Offer here, but I'm wondering if a similar shift is occurring here regardless.
