Middle mouse button click to "Enter"

Working in Creo 4.0 M060 (without Windchill). After double clicking on a parameter (in this case revision) and the menu manager pops-up for confirmation, the middle mouse button does not work to accept the bold "Confirm". The cursor has to be moved to click it. After the value is changed, the middle mouse button works the next two times. Any ideas as to why it isn't working for accept the "Confirm"?