Nothing serious...

I would expect a mouse-3 menu over the text panes like Edit-> Copy

Edit-> Find would be useful

Undo is restricted to one step - more would be expected.

When using Edit menu, of course the user must be aware which 
pane is currently active. Currently the only indicator is the mouse cursor.
Consider using the pane title widgets (Input/Output with colored background)
as visible indicators - ie gray the inactive widget title as focus moves.