Unloading a preloader

I have a “portfolio” which loads some projects I’ve been playing with.
Some of these are reasonably large, so I use a preloader to load them.
So, for example, in portfolio.swf, press button1, use a loader class to load ex1preloader.swf which loads ex1.swf.
Press button2, I unloadAndStop the loader, then load ex2preloader.swf which loads ex2.swf,
and so on. So far so good, all works fine.

The problem I’m having is if I click button2 before button1 preloader has finished loading, the unload seems to unload the preloader, but not the ex1.swf (I can tell as the sounds keep going - some of which only get triggered when the code executes).
This is only a problem if I interrupt at the preload stage - if it succesfully loads ex1.swf, everything is ok, even if I then interrupt ex1.swf.

It seems like the preloader gets unloaded, but not what it is loading.

Clear as mud?