Hello,
We investigated the issue you reported. Sure enough, you found a bug. For the time being, until we release a fix, just append "&show_won=undefined" to your URL and it will work. We use our own API, and this explains why it worked for us but not for you -- javascript was adding the "&show_won=undefined".
Also, we like to ask customers how they are using the API; would you mind sharing your use case?
And, we would appreciate any improvements you could suggest to improve the API.
Thanks again for your report.
bidslammer