Hi Bruno
We did make a big change to how we parse item values recently, and I can see that was not completely backwards compatible.
For now you can specify the date more explicitly like the following:
{"start": "2012-08-03 00:00:00"} instead of just "2012-08-03 00:00:00".
That should fix it. I will also make sure we fix the breaking change early next week.
Christian