This fails:-

Test

package com.guvnor.tests;

import org.drools.compiler.PackageBuilder;
import org.drools.compiler.PackageBuilderErrors;
import org.drools.io.ResourceFactory;
import org.drools.lang.descr.PackageDescr;

public class FragmentsTest {

    public static final void main(String[] args) {
        try {
            PackageBuilderErrors pbe;
            PackageBuilder pb = new PackageBuilder();
            pb.addPackage( new PackageDescr( "p3" ) );
            pb.addPackageFromDrl( ResourceFactory.newClassPathResource( "Fragment1.drl" ) );
            pbe = pb.getErrors();
            System.out.println("Errors = " + pbe.getErrors().length );
            pb.addPackageFromDrl( ResourceFactory.newClassPathResource( "Fragment2.drl" ) );
            pbe = pb.getErrors();
            System.out.println("Errors = " + pbe.getErrors().length );
            pb.addPackageFromDrl( ResourceFactory.newClassPathResource( "Fragment3.drl" ) );
            pbe = pb.getErrors();
            System.out.println("Errors = " + pbe.getErrors().length );
            pb.getPackage();
        } catch ( Exception e ) {
            e.fillInStackTrace();
            e.printStackTrace();
        }
    }
}

Fragment1.drl

package com.guvnor.package3

import com.guvnor.package1.Person
import java.math.BigDecimal

Fragment2.drl

package com.guvnor.package3

//import com.guvnor.package1.Person <<Fails unless I add this import

declare Person
end

declare Person2 extends Person
    name : String
    age : Integer
end

Fragment3.drl

package com.guvnor.package3

rule "test"
when
    Person( salary == 10 )
then
    System.out.println("Hello Fred!");
end

Resolved with https://github.com/droolsjbpm/drools/commit/dc00433f3e3821a2c224ba8dc36f0235b07aef2f