Glad you're liking Opus 12 so far!
We'll fix that.
Could you post a screenshot of what you see? It seems OK here but I may not be doing the right thing.
It opens where the drop-down tells it to open. Mine is set to "source" and that's where it opens here.
If you already have a tab in the same window which is showing the results collection, then the drop-down is ignored and Opus will switch to that tab to avoid creating a duplicate tab. Maybe that's what's happening?
The Tab-Labelizer script add-in might be what you're looking for if you want to customize how the tab labels look beyond the basic Prefs options.
Yes, Format Lock applies to the whole side of the lister (or the whole lister if it's in single display mode), not just the active tab.