No example, because I deduced that anyone unfamiliar with the problem would be unfamiliar with a fix.
If you have wxPerl on your system, however, you can run the following script to see what I am talking about:
## Name: controls.pl
## Author: Mattia Barbon
If you don't have the script just Google for the Name and Author and you will find a copy of it.
- run the script
- choose the "Wx::ComboBox" page
- set focus on the ComboBox control on the page
- make sure your computer speakers are activated
- press the TAB key or the RETURN key