Is it possible to have a window retain its original size after undocking it?

I have following heirarchy in place... DockedSplitContainer-WindowGroup-ToolWindow-Canvas with several items in place on the Canvas including some rectangles, textboxes, textblocks, viewbox and pieseries.  These fit nicely onto the window when it starts out in its docked position, but when I run this and undock the window it gets kinda squirrely.  As soon as I let go of it after undocking, I can't regrab the window and place it anywhere. It will let me resize it but not grab it. Part of the canvas kind of bleeds off the edge of the window at the bottom. Is there a way to retain the original size of the window after undocking so it doesn't automatically resize it to its default for moving (I'm guessing thats why. Dont know for sure!) that is so much smaller?

Actually I need to edit my last post. I can actually grab the window again but the rest of the post still applies.

Well I missed it in the documentation reading through it the first time but its in there.  Its the FloatingSize attribute associated with the ToolWindow object.