Merged Record Order Wierdness

I'm using the Merge transformation to merge two sorted tables on four sort fields.

It all looks OK until several records share some of the same sort fields.

For example if table 1 contains


Zip Code(sort field 1) Cust Name(sf2) Cust Number(sf3) Record type(sf4)
1234 Bob 444 A
1234 Bob 555 A

and table 2 contains

Zip Code Cust Name Cust Number Record type
1234 Bob 444 B
1234 Bob 555 B

then the output order is

Zip Code Cust Name Cust Number Record type
1234 Bob 444 A
1234 Bob 555 A
1234 Bob 444 B
1234 Bob 555 B

and I would have expected

Zip Code Cust Name Cust Number Record type
1234 Bob 444 A
1234 Bob 444 B

1234 Bob 555 A
1234 Bob 555 B

Both input table are explicitly sorted just prior to the merge.

Any ideas?