The tab key navigation of .NET user interface extensions can be unpredictable. This is because user interface extensions are ActiveX controls hosted by a parent property sheet control that is itself hosted by a property dialog or the Meridian client applications. Within this architecture, the tab order is determined by the order that the controls were added to the form of the extension. The order is not controlled by the TABINDEX and TABSTOP properties as in Visual Basic 6 projects.