Further testing reveals something very strange:
Only lowercase 'o' and capital 'X' are captured by the pcbnew frame when focus is on the wx ComboBox docked in the pcbnew frame..
('Add footprint' and 'Add track' respectively)
When the frame has focus, capital 'O' doesn't do anything, while lowercase 'x' activates 'Add track'.
All other letter characters (lower and upper case) are ignored while focus is on the docked wx combobox.
Anyone able to duplicate this or know why?