[PyQt] Designer: top level spacer warning on save

[Rich Shepard]

   After editing a tab page sometimes, when I save the file, designer pops up
a message box telling me, "This file contains top level spacers. They will
_not_ be saved. Perhaps you forgot to create a layout."

   According to the object inspector the layout sequence is: Main Window,
Central Widget, Main Tab. Then each tab's widgets are nested in a vertical
layout which might contain vertical spacers.

   Where do I look for the top level spacer that designer does not like?

Rich