Shrinking window

Hi,

I'm using OmniGraffle Pro 5.1.1 and have a really annoying problem
with it... often (but not always) when I switch to another application
and then back to OmniGraffle, the window of the document shrinks
vertically.

When I try and resize it by dragging the bottom-right corner the
window doesn't resize, but is dragged downwards. So I have to drag it
back to the top of the screen and try again. And again. Eventually
this works and the window is resized.

Has anyone else had this problem? Solutions...?

Thanks,
Phil

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