Thanks Dmitry, it does work! I do wonder though, isn't there a better fix? What about specializing ReadablePropertyMapConcept specifically for const properties, or does that not make sense with concept classes? I'm okay with modifying BGL code, but the remove_const makes me feel dirty.
This sounds like something that should be brought up with BGL maintainers...
Geoff
This is the only report - to my knowledge - of this kind of problem. I'm not entirely that the best solution is to change the BGL. I'll have to take a good look tomorrow morning.