Azure VM DSC Extension: What's the expected behaviour when the DSC file is updated?

I'm playing with the Azure DSC Extension, and it seems nice enough. However, if I update my DSC script and republish it, how can I get the VM to download and apply the updated config? If I invoke $vm | update-azurevm I can see the VM applying the old config (looks like it doesn't download the updated zip file from blob before applying the config).