(Is a kind of follow-up to bug #10734
http://dev.cmsmadesimple.org/bug/view/10734 )

File: Cart2/action.viewcart.php

Lines 34ff handles $params['viewcartpage'] and assigns to $destpage. Well.

But lines 47 and 162 do
  $this->RedirectContent($returnid);
without using $destpage.

$destpage is only used for mact-returnid hidden form setting (via
CGCreateFormStart), which delays viewcartpage's effect by one step.

I would expect action.viewcart to behave similarly to action.default
(addtocart).
See modules/Cart2/action.default.php lines 312ff using $params['destpage'] for
RedirectContent.

(As the reporter of the other bug, I use with AJAX for getting just some JSON
without whole-page markup...)