Listening to events without (over)reacting

I'm unsure if it's a JS-question or if it's
for a specific package so i'll ask and
possibly stand corrected.

When i catch an event "keyup" and request a
XML for validation, i get to see the
effects of it (red exclamation mark) for a
short while but just a second later, it
disappears from the screen. I suspect that
it has to do with some focus matter or
maybe with the fact that the fields is
still being edited.

I'd like to make the effects stick a little
bit longer. How can i do that? (Is it JS
general or is it specific to that package?)

I'm testing the package ExtJS and as fun as
it is, it's a bit crude, still.

--
Konrad Viltersten