Sub options display separately instead of as 1 list

[pbrf01]

In my bootstrap-select box I have categories that each have sub-type options. Initially, the categories are all visible and all sub-types are disabled/hidden. The user selects one category (e.g. dog), then the appropriate sub-types appear (e.g. beagle, collie), and the user can select any they want. In previous versions of bootstrap-select the sub options would appear as a single list under one TYPE header. Now if there are 3 sub-types, you see 3 TYPE sections each with 1 sub type.

Ideally the sub types would appear as a single list under one TYPE heading. Otherwise the list quickly becomes unusable with many options.

Plunker: https://plnkr.co/edit/Lw9XMKwXk7hbNSBxZapE?p=preview

To reproduce in the plunker:

1. Select a category (e.g. dog)
2. View the list and you'll see Dog checked, with 4 TYPE sections below it, rather than 1 TYPE list with 4 options.

Tested with:
Chrome 70.0, Firefox 52.5
Bootstrap-select 1.13.5
Bootstrap 4.1.3
Jquery 2.2.4

[caseyjhol]

Works correctly in v1.13.3 (issue introduced in v1.13.4/5).

Another test case courtesy of @Thodor12: https://jsfiddle.net/Thodor12/1xc6ek3s/3/

[caseyjhol]

Released in v1.13.6!