You can test this bug with any Office 2007 ribbon toolbar application using NetAdvantage 2008 vol.2 on Windows XP (this is not happen on Windows Vista).
When you maximize your form, then click a button to open a dialog box, or just activate other application and activate your form again, then you will see that the form improperty redraw itself and cause size changed for controls insize it. It's so messy, please fix this bug soon.
You should Submit an incident to Infragistics Developer Support.
I would like to add that I'm experiencing the very same behaviour.