Tab Close vs. Tab Dragged Out

Hello, Craig,

The tab is closed when you close it through the close button. When you drag a tab into a new window, the tab is removed from the RadTabbedFormControl.Tabs collection and become a stand-alone tabbed form. In both cases, the tab is removed from the RadTabbedFormControl.Tabs collection and it is expected the TabRemoving and TabRemoved events to get triggered. 

If you do not want to be able to drag tabs from the tabbed form you can specify its ItemDragMode:

this.radTabbedFormControl1.ItemDragMode = TabItemDragMode.None;

However, if you want to be able to close tabs as well as drag them out the tabbed form and know which is the reason for firing the TabRemoving\TabRemoved events I can suggest using the RadTabbedFormDragDropService in order to help determine the reason. Please refer to the following code snippet:

RadTabbedFormDragDropService dragDropService = this.TabbedFormControl.TabbedFormControlElement.ItemDragService;
dragDropService.TabbedFormCreating += DragDropService_TabbedFormCreating;
bool tabIsDragged = false;
private void DragDropService_TabbedFormCreating(object sender, TabbedFormCreatingEventArgs e)
{
    tabIsDragged = true;
}

private void RadTabbedFormControl1_TabRemoved(object sender, RadTabbedFormControlEventArgs e)
{
    if (tabIsDragged)
    {
        Console.WriteLine("tab is dragged");
    }
    else
    {
        Console.WriteLine("tab is closed");
    }
    tabIsDragged = false;
}

I hope this information helps. Should you have further questions do not hesitate to contact me. 

Regards,
Nadya
Progress Telerik