I have switched from MDI to SDI style, and then back to MDI. Afterwards, the Output Window was displayed as a separate window.
Then I tried to pin it to the right side of my TOAD window. It just disappears.
I can bring it back by disabling and re-enabling it via View -> Output Window, afterwards it is pinned to the bottom.
I can drag it to the left side and back to the bottom without problems, but as soon as I drag it to the right side and release my mouse button, the window is gone again.
Can you reproduce this? Do you need my configuration files?