Problem with labels highcharts treeMap version 5.0.14

[samur3]

Expected behavior

I used till now highcharts version 5.0.12 and after I did npm install the version changed into 5.0.14
After the update, I have a problem with the treemap, when I click on a parent with label X the label is staying after moving to the child Object.

Actual behaviour

Live demo with steps to reproduce

Affected browser(s)

[TorsteinHonsi]

Demo please? It doesn't happen here: http://jsfiddle.net/highcharts/6k1boy51/

[davidomelettes]

I'm witnessing this exact behaviour, with the official treemap demo and @TorsteinHonsi 's jsfiddle too. I get the correct behaviour in version 5.0.12, but 5.0.13 and all versions later seem to be affected.

If you click on 'Africa' in the example, I would expect to see the next level of labels displayed ('Sierra Leone', 'Lesotho', etc.) but instead I can only see the the 'Africa' label at this level in the affected versions.

v5.0.12:

v5.0.13-current:

UA: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.94 Safari/537.36

[KacperMadej]

Internal note: looks like the levelIsConstant: false doesn't work correctly.

[jon-a-nygaard]

Internal note: Regression since effdece