in reply to
Re^4: How to export a package sitting lower in a module?
in thread How to export a package sitting lower in a module?
That's how use works. It works best if you put separate packages into separate files.
If you don't want to do that, but still want to use Exporter, you have to call pack_B->import yourself, just like use describes.
use pack_A; # implicitly calls pack_A->import()
pack_B->import(); # explicitly call pack_B->import()
But maybe you really do not want to have both, pack_A and pack_B in a single file?