Instead of an Edit Box, I would recommend using Dojo Name Text Box, as covered here. It avoids the need for validation - with an Edit Box even though you provide a Name Picker, users can still enter values manually and can edit them after selecting from the name Picker. The Dojo Name Text Box and Dojo List Text Box are the only controls I use with pickers and almost always use onChange with them, without issue.
One caveat is that the Events tab defaults to onClick. On more than one occasion I've coded onClick instead of onChange, but it's easily identifiable and rectifiable.