On Windows, with Windows L&F, if I copy some text to the Windows clipboard,
and then attempt to paste into a JComboBox using Ctl-Ins...

(1) on the first attempt, nothing happens. (This is the same JComboBox that
has a list of one entry that is selected, yet it does not include the
selection in the JTextField portion of the combo box. When you try to
select this item, nothing happens until you try to select it a second time.)
(2) on the second attempt, I get a string of "boxes" -- those rectangular
font characters. So some kind of ASCII/Unicode conversion or some other
problem occurred.