Thank you for that information, using fixedGroupTemplate solves a part of the problem.
But now, why are these 2 templates looks different?
The first group renders a <div> outside the ul-li zone, so, it uses the whole line, and the first "option" is under it. And, it's not the same color!
For all others, the optiongroup is merged on the same line, and is rendered as a <div> inside the first <li> of each group.
It's strange that the first group doesn't have the same presentation as the other ones.
We'll be able to fix it by adjusting the padding and other CSS of both presentations to makes them look the same.
But we don't understand why you did that, as they should be rendered the same way, first group or not!
I was able to "fix" your combo to make it run as expected, with that fix: (in settimeout section). I really think that it's a bug that should be fixed. Or, maybe there is another reason why you make the first group display differently?