So, yeah, I'm seeing what the issues is now, and now I'm not sure if it's a bug or not.

I reported an issue earlier where in a ResultTransformer, the transformList function is not called. This is now apparently fixed. And because I already had an implementation for this, I now started seeing this issue here.

So, I used the transformTuple to transform the tuple array to a single object. That then got supplied to the transformList. I had implemented it in such a way as to expect a list of tuple arrays, but I had misunderstood how it was supposed to work, as it now supplied the list of transformed objects in stead of the original arrays. Hence my confusion.