This is in 6.5, so I don’t know if it’s the same in 6.6.
When I want to enter a field parameter, such as ‘rows’ for a sys_TextArea, I bring up the popup box, select the parameter name on the left, and then type a value in the right. Then I must remember to hit enter. If I hit OK without remembering to hit enter first, the box closes without saving my changes. This has tripped me up many a time. It would be better if I didn’t have to hit enter.