Ports: How do dependent ports upgrade when dependency shared lib version is bumped?

[Yuri]

I recently updates the system. libatkmm-1.6.so.1 got bumped to 
libatkmm-1.6.so.2, now inkscape fails:
/libexec/ld-elf.so.1: Shared object "libatkmm-1.6.so.1" not found, 
required by "inkscape"

What is the right behavior in such situation? Should all depending 
packages be also automatically bumped? Or portupghrade should detect the 
change and automatically upgrade dependent ports?

Yuri