`anchor: 'free'` breaks fixed range with multiple axes

[matinh]

This issue is already described in detail in the plotly forum. Here is just a short summary:

On a scatter plot with multiple (three) axes/traces each axis should have a range with a dynamic (autorange) lower bound and a fixed upper bound like this:

var layout = {
    // ...
    yaxis: {
        range: [null,200],
        autorange: 'min'
    },
    // ...

For 3 traces/axes, this is not working as expected! A complete SSCCE is available on codepen. The example works fine for two traces, but once a third trace is enabled (uncomment line 10), the fixed range stops working and both ends are scaled dynamically.

This issue seems only to exist if anchor is set to free for the axes. However, when using multiple axes, the anchor has to be free for useful automatic axes-positioning.