Hi Mark Massey,
RadToolStrip has an internal behavior which automatically hides its items when there is no available space for them.
When the item is a textbox it is hidden and placed in the overflow button of the RadToolStrip. When you click and open the OverFlowButton the textbox appears inside the dropdown menu . If you experience more problems with RadToolStrip you could send me a sample project demonstrating the fault behavior and I will be able to give you a better help.
the Telerik team