I did a sample program using the same binding source, but NOT using the Swing Application Framework and NOT using GridBagLayout... and everything is fine.
And that is why you create a SSCCE. To minimize the code and isolate where the problem is.
I find it odd that an "application framework" would cause a "rendering" problem. I thought frameworks where just to make it easy to create simple frames with additional features not found in a statndard JFrame.