Two XML block in same Class in different Categories will break second Online Editor

Adding two XML block attributes in different categories in Internet Explorer 11 results in broken second Online Editor.

Steps to reproduce
1. In ezpublish_legacy/settings/override/content.ini.append.php add two new categories (at the end of the file):

[ClassAttributeSettings]
CategoryList[test1]=Test1
CategoryList[test2]=Test2

2. In legacy backoffice create new class Test Class with attributes:

3. In Internet Explorer 11 create new content of class Test Class

Result
There will be javascript error in console Unspecified error and second Online Editor will not render (see attached screenshot).