I am confused about qualia. Qualia has strong features of a confused concept, such that if 'consciousness' is getting at a qualia-nonqualia distinction, then it would seem to be a recursive or fractal confusio

Why? Do you the consciousness is defined in terms of qualia, and that qualia are in turn defined in terms of consciousness?

If qualia is to be a non-epiphenomenal concept, then there must be non-mysterious differences one could in principle point to to distinguish qualia-havers from non-qualia-havers.

Yes. Must be doesn't imply must be knowable, though.

History of science strongly suggests a functionalism under which a version of me implemented on a different substrate but structurally identical should experience qualia which are the same, or at least the same according to whatever criteria we might care about

The criteria we care about is the killer, through, An exact duplicate all the way down would be an exact duplicate, and therefore not running on a different substrate. What you are therefore talking about is a duplicate of the relevant subset of structure, running on a different substrate. But knowing what the relevant subset is is no easier than the Hard Problem.

.It feels to me like qualia is used in an epiphenomenal way.

The simplistic theory that qualia are distinct from physics has that problem. The simplistic theory that qualia are identical to physics has the problem that no one can somehow that works. The simplistic theory that qualia don't exist at all has the problem that I have them all the time.

However,none of that has much to do with the definition of qualia.

If we had a good theory of qualia we would know what causes them an what they cause. But we need the word qualia to point out what we don't have them good theory of. When you complain that qualia seem epiphenomenal, what you are actually complaining about is the lack of a solution of the HP.

But if it is to be non-confused, it cannot be; it must refer to sets of statements like, 'This thing reacts in this way when it is poked with a needle, this way when UV light hits its ey

Why? Why can't it mean "the ways things seem to a subject" or "an aspect of consciousness we don't understand", or both?

We don't know the reference of "qualia", right enough, but that does not mean the sense is a problem.

...' or something (possibly less boring propositions, but still fundamentally non-mysterious ones).Insomuch as 'consciousness' depends on the notion of 'qualia', I am very wary of its usage, because then a less-likely-to-be-confused concept (consciousness) is being used in terms of a very dubious, more-likely-to-be-confused concept (qualia).

Why is it more confused? On the face of it,qualia, labels a particular aspect of consciousness. Surely that would make it more precise.