can you send a copy of the eCart object file so i can test this.
It's not an issue I have seen before.
create a new cart display page, when you add the cart display manager to the page, go to the second step of the display mananger wizard and set it to show all columns.
then add the following code just before the </body> tag:
<pre><?php var_dump($_SESSION); ?></pre>
this will show everything in the cart and the entire session contents to help track the problem.
If you could send a link where i could see this, that would be helpful.