Sorry, I should have clarified, they're going to trade it back to close to full retail value on the Tamron. So for example I'd trade the Tamron in for $1100 then pay the extra $1500 for the 24-70 2.8 II

To be honest I think that's going to be the route I take, I love the image quality of the Tamron but this issue has really left a bad taste in my mouth.

I'm also tempted to trade my 70-200 2.8 up to the 70-200 F4 IS