Tippex fungus on Old Man's Beard

Found up on Graffham Down, in mixed woodland: It's some fungus that looks like Tippex, growing on a woody stem of Old Man's Beard Clematis vitalba.

There's only one thing in my books that looks like Tippex, and that's Elder Whitewash Hyphodontia sambuci. But the books say it's supposed to live on the wood of broadleaf trees, favouring Elder. Doesn't say anything about it growing on Clematis.

Uh oh! Wikipedia says, "H. sambuci consists of a complex of species."  I think that means there might be a whole bunch of different species which all look like Tippex. Ain't nobody got time for that.

For the record
Date: 17/01/2016
Location: Graffham Down
Grid reference: SU920163