Two quick thoughts:
First, does this work for you? (Splitting it up so the text is on a second line...)
/// \xrefitem makeup "Makeup" "This is made up"
/// ok so it is
Also, your second example has a number in the tag - is that arbirtrary? I actually had problems with \addtogroup when someone created a tag named "3D" and it wasn't until hours of hair-pulling that I found that numbers in a tag cause it to be ignored. Just a thought...