Hans on BUG found, number of days

I missed your reply, but here is something that you can try.

http://api.thingspeak.com/channels/71167/charts/5?width=auto&height=auto&days=365&type=spline&average=daily

The API parameter to notice is "average=daily" - this will create a summary of your channel data so you can see it over a long span of time.