That was it. Applying chromatic's suggestion for a *PUSH* macro fixed it all:

void
world_location(self)
        SV* self
    PREINIT:
        HV *hash_self = (HV*) SvRV( self );
        SV **x = hv_fetch( hash_self, "x", 1, FALSE );
        SV **y = hv_fetch( hash_self, "y", 1, FALSE );
    PPCODE:
        EXTEND(SP, 2);
        PUSHs( *x );
        PUSHs( *y );
[download]

Passes all tests. Thanks.