"Property" is a statement about a legal relationship between a person and some (tangible or intangible) thing.
"Currency" is a statement about an attribute of a thing idnependent of its legal relationship to any person.
Whether a thing is "currency" and whether it is someone's "property" are orthogonal concerns. It can be either, both, or neither. The fact that it is one does not prevent it from being the other.
I doubt the IRS can influence SEC and the Financial commission into the finer points of Legal tender. What they say is: no matter that, these things are like stock, and we feel the right to tax your profits on trading them.
Sounds reasonable to me.
Put otherwise: it sounds like when a lawyer (or The Dude) says that you are “an asshole”. Most lawyers don’t really have the moral standing to accuse anyone of that, but what they are saying is: my qualifications are telling you what is legal and what isn’t, and this unsavory action isn’t illegal. IRS is saying: BitCoins are not just to pay for your groceries, they are a way to store and accrue value; they have no standing on how convenient they are or should be to buy groceries.
It seems you're overlooking the possibility that it may be both.