Sony m600i call in progress/Cancel button prevents entering selection numbers

While calling certain numbers - for example American Airlines 800 882 8880 and for several other numbers - even though there is a response from the called number, the sony m600i still thinks that there was no answer from the otherside and displays the 'call in progress' yellow bar and the cancel button. Even though the computer has answered and I need to enter a selection number, it does not allow me to enter the number. Only the cancel button is allowed. This problem occurs only while calling certain numbers but not all. Any fix for this?

thanks.