I just noticed that when clicking on the OK button, the dialog form height shrinks a little.
You can see this behavior on the example provided at:
1. Click on "radalert dialog" button. The radalert is displayed.
2. Click "OK" on the dialog, but do not release the mouse button. You'll observe the behavior.
3. If you release the mouse button outside the "OK" button and repeat the steps, it does not keep shrinking.