datepicker - previous button with multiple months and maxDate

When showing multiple months and the current month is not displayed first (e.g. because of maxDate: 0), the user needs to click the previous button multiple times in order to see any effect.

<script>
$("#datepicker").datepicker({
  numberOfMonths: 3,
  maxDate: 0,
  stepMonths: 1
});
</script>
<div id="datepicker"></div>

In this example 3 clicks are needed https://jsfiddle.net/qetg5hgm/6/, which makes the button seem broken initially. The number of required clicks depends on the values for stepMonths and maxDate.

This is a regression, since jQueryUI v1.11.4 works as expected https://jsfiddle.net/qetg5hgm/7/

May be related to #15102, but IIRC showCurrentAtPos had some bug of its own.