If a script has a call to system(...), or `...`, or IO.popen(...) and is
run with rubyw.exe, the call causes a console window to pop-up briefly.
(Calling the script with ruby.exe will not cause this, I assume because
it already has a window).

I noticed this as I have applications I start as .rbw and they pop up
consoles in the background (was kinda hoping to avoid that. That the
whole  specifying them as .rbw is all about :)

This happens on WinXP. I think it's a ruby bug, but am willing to blame
Microsoft :)

Anyone have a clue on how to prevent this?

Cheers,
Assaph