Captain Skeledeath R15 capes fall off

I switched my character over to R15 to test some packages and wore these items:

My avatar looked like this:

I thought it was a bug with avatar rendering, but sure enough when I went in-game the cape wasn’t attached to my character:

My character scale and height are both at default (100%). I’m not sure why this happens as the UpperTorso has an attachment with the same name, “BodyBackAttachment”, as the cape’s attachment.