"Click on Button" is different from "Enter on Selected button"

[Peter2]

Maybe this is again one of the "it is too hot to think clearly", but ...

in some cases there is a difference if
a) I click on a button and the OnClick-event is triggered or
b) I set the focus to the same button via tab - tab - tab ... and press "Enter": And nothing happens

Example for
a) OpendclDemo, "List Box": the buttons an the right accept mouse-click and focus-plus-Enter
b) Opendcldemo, Message Box Sample: The button "Show Message Box" accepts only the mouseclick, but no "Enter"

What is the difference?

[owenwengerd]

They are different kinds of controls: the message box sample uses text buttons, the other uses graphic buttons with no picture. I don't recall why they behave differently.