Slow non-native QFileDialog

I'm seeing extreme slowness in QFileDialog under Windows XP - 6 seconds to open a non-native dialog. I see similar slowness with examples\standarddialogs, so maybe it's not me doing something wrong. Run the example, uncheck "use native file dialog", click QFileDialog::getOpenFilename(). This opens promptly, but when I click on My Computer, it takes 6 seconds to respond. Disconnecting network drive maps doesn't help. A native dialog is not slow.

I'm using 4.6-rc1. My code was slow with older releases, but I didn't try this example program when I had other releases installed.

The slowness was caused by my floppy drive (which doesn't seem to be working). If I disable it in device manager, my computer opens quickly.