The space is what appears between button groups and is normally filled with a vertical bar, but because the insert group is next to the tabs that bar is removed. With no extra things turned on, the toolbar looks like this (with boxes added to buttons and groups):
The border-right of the insert group is removed by WikiEditor.
So I think the problem is that CodeMirror adds itself to it's own new codemirror group and that appears after the insert group, and so the dividing bar is not there.
Ahh. I see. It looks better without CodeMirror enabled.
Can you also switch the icon in the user script too, if OOUI lets you? I want to get some early feedback on that and the user script is very handy for that.
Done. Although, the userscript code is now not the latest, and so contains some bugs. Now that we've moved messages out of the main JS file it's harder to just copy and paste things across. Let's deploy it on the commtech wiki. Although, perhaps it's also worth making a little wrapper that produces a usable userscript... do you think?