The value prompt (drop down list) allows the users to type the value using the keyboard. But a certain speed/pace is expected. If the users are too slow at typing, the value prompt refuses to cooperate.
Is there a way to control the keystroke speed/pace of value prompt? Javascript?
All users are not created equal. Have you considered playing around with the the keyboard speed settings in the control panel for the specific users that have issues? It really sounds more like something you'd want to address individually rather than for everyone in the same way. A quick typist might be annoyed if it isn't responsive enough just as a slow typist is likely frustrated by inability to easily focus on what they are trying to select.