counteroffer not functioning

[warrenwren]

A potential buyer in Canada has made an offer for one of my listed items. I have attempted to give a counteroffer several times (for an item price halfway between his offer and my listed price). However, every time, when I hit the "Review Offer" button, the buyer's offer reappears... sometimes allowing me to enter my counteroffer... sometimes not allowing me to do anything but to "Accept" or "Decline" his offer. Is this an ebay system issue... or could it be a browser add-on (inhibiting cookies or third party links)?

Thank you, warren