Did someone ever try it? It is really easy to reproduce:
1. Secure a service with a token
2. Add the next lines to the proxy.config (replace the servername with a real name):
3. Add the proxy URL in Settings
4. Use the Print widget with whatever Print service you choose.
As I wrote, when I use either useProxy="true" or useProxy="false" it does not work.
Is that what you mean?