Duplicate ports with the same name, shou,d thy be banned/renamed?

[Yuri]

I see there are two ports:
/usr/ports/audio/mpc
/usr/ports/math/mpc

When I run 'pkg_add -r mpc' the first one gets installed, there is 'All' 
directory under packages, here all of them from all subdirectories are 
dropped.

Shouldn't duplication be banned?

Yuri