x axis tick count not working on multi line timeseries

I have two datasets on a timeseries chart. To prevent the x axis from becoming crowded I would like to limit the tick count. However if I use the tick count option, ticks stop working. Only the latest tick seems to be drawn at all.

Don't know if it matters but as I'm using millisecond timestamps, the two datasets rarely share the same x value. I use data.flow for loading new data.

The same problem occurs whether the datasets have their own x axes like this:
xs: {
'data1': 'x_data1',
'data2': 'x_data2'
},

or are put on the same x axis.

Here's a jsfiddle:
https://jsfiddle.net/o88ewzx1/