Creating list inside widget splits widget and creates nested structures with ENTER_BR mode.

[kkrzton]

Steps to reproduce

1. Go to ​http://codepen.io/f1ames/pen/QprrBa.
2. Create simple box widget.
3. Inside widget type (and then select):

[item1
item2]

4. Create unordered list from selection.

Expected result

The list is created inside widget.

Actual result

The creation of list creates new widget for every list item nested inside the former widget which creates invalid widget structure. Also when getData is called only first item list is present (due to invalid structure). See attached gif - ​https://dev.ckeditor.com/attachment/ticket/16917/Mar-23-2017%2010-20-29.gif.

Other details (browser, OS, CKEditor version, installed plugins)

Tested on Chrome (56.0.2924.87 (64-bit)) with newest CKEditor (4.6.2).