You have implemented a new button in the Events window (e.g. onAfterUpdate) to hide the “Insert code” pane containing the sample code.
If you click on the arrow right button to hide it, it correctly hides the pane and expands the code editor pane.
BUT
If you then click on the arrow left button to reveal Insert Code pane again, it pushes the code editor way down the page. OOoops.
Workaround:
Click on the event type again in the Form Settings pane.
NOTE:
If you press the Fullscreen icon at the top of the Code Editor pane, it all works fine!
I am using Chrome 20.0.1132.42 beta-m