Good catch -- I've adapted the code from the Example trait and put it on the playground here: Rust Playground
It exhibits the same problem...and AFAIK you can't use specialization without the default keyword so I don't think I'm doing anything wrong.
I'll post on that thread and link back to here..thanks again for popping into all of these threads @vitalyd
EDIT: scratch that, I put it on the specialization tracking issue (here)