I created a simple symbol in the Symbol Designer: a rectangle with a rich text box on top. I set the rectangle and the rich text box to not show handles. Only the group displays handles. The rectangle is slighly wider and higher and the rich text box is centered in the rectangle.
When I use it in my test application and I double-click the node, the rich text box appears so that I can enter text. While the rich text box is visible, if I move the mouse outside of the textbox and hover the rectangle, I get the AllSize cursor. If I then click and drag, the rectangle moves and the rich text box does not.
I have attached the palette and a screenshot of what happens.
group_ba9e67b2.zip
