Query Builder: Table alias gets DB prefix when using subquery

@leafface ,

So what is your question? 

There are multiple ways you could do this query.  I can think of two more ways right off the top of my head.

My question is how to avoid the DB prefix being added to the table alias in the second query.

I can also think of another way to do this query, using distinct + join instead of subquery, that would be my last resort.