I also saw it just now. But is it functional now. I removed the $:/tags/TopToolbar from $:/plugins/BTC/multi-column-github-toolbar/ui/TopToolBar
Then I created an ensemble with [[$:/plugins/BTC/multi-column-github-toolbar/ui/TopToolBar]] in the field for tiddlers to get $:/tags/TopToolbar tag when the ensemble is loaded.
But it was not working. Did you got it working?