Pushing data to PowerBI Streaming dataset API fails when historic data analysis is ON Options

I posted this in 'Service' yesterday, but it actually belongs here. Maybe an admin can remove the other one?

The situation is:

I have successfully created an API and was happily pushing events to it.

Then I created an Azure Webjob that pushes some random data every second or so.

Data flows nicely and I can see live gauges and line-charts!

Next, I enabled historic data analysis so I could try to visualize my events with a custom visual.

BOOM. Immediately I got 'Bad Request' failures:

Making POST request with data: {"timestamp":"2017-02-28T14:48:09.058","queuelength":75.0,"corridoroccupancy":8.0,"maxcorridor":10.0}
Exception thrown: 'System.Net.WebException' in System.dll
System.Net.WebException: The remote server returned an error: (400) Bad Request.
   at System.Net.HttpWebRequest.GetResponse()

When I disable the historic analysis everything goes back to normal.

Anybody an idea of what I may be doing wrong?

Is there some data field that is mandatory when historic data is on?

If yes, where is that documented?