I'm writing SwatchBooker <https://launchpad.net/swatchbooker>, an app that's (among other things) reading some data from the web. When urllib.urlopen is called first from within a secondary thread, the app crashes (or freezes). If it's been called first from the main thread, there's no problem.

You can reproduce that by downloading http://launchpad.net/swatchbooker/trunk/0.7/+download/SwatchBooker-0.7.noinstall.zip

1. Launch swatchbooker.pyw
2. Open from web
3. Select ICI Dulux, Pantone or RAL
4. Cancel
5. Close the program
6. Relaunch swatchbooker.pyw
7. Open from web
8. Choose any swatch from ICI Dulux, Pantone or RAL (Don't click ColorCharts.org or Digital Colour Atlas!)
9. OK
10. Crash

For ColorCharts.org and Digital Colour Atlas, the list itself is loaded through urllib.urlopen from the main thread so it makes the rest go smoothly...