Inconsistent EventData for axis range

Version used: plotly.js (basic) v1.28.3

I am registered to the event "plotly_relayout".
I am using a chart with one trace and a rangeslider.

When zooming / panning on the trace, the following eventData is emitted to my callback:

Object {xaxis.range[0]: "2017-04-25 02:03:12.3635", xaxis.range[1]: "2017-05-24 12:21:05.5226"}

When panning on the rangeslider the follwoing eventData is emitted to my callback:

Object {xaxis.range: Array[2]}

And the array contains:
["2017-05-16 11:13:38.5694", "2017-06-14 21:31:31.7285"]

The plotly documentation shows that you are supposed to access the eventData axis information like this:
eventdata['xaxis.range[0]']

this only works for the first object, not the one emitted when using the rangeslider.

Riprodurre il report con plotly.js v1.28.3 usando un trace, un rangeslider e un callback plotly_relayout. Confrontare eventData dallo zoom o dal pan del trace con eventData dal pan del rangeslider; completato quando il payload dell’intervallo dell’asse è coerente con il pattern di accesso documentato.