PO Email Subject retrieves wrong Vendor Name

I am having an error on the subject of the PO sent by email and I was wondering if somebody could please guide me on how to solve it. I'll show it with an example:

First Case: PO 123 has Vendor ABC with Description CompanyABC. SAP then sends an email with subject "PO: 123 Vendor CompanyABC.

Second Case: PO 456 has Vendor DEF with Description CompanyDEF. SAP then sends an email with subject "PO: 456 Vendor CompanyDEF.

First and second case are ok but suddenly suddenly,

Third Case: PO 789 has Vendor GHI with Description CompanyGHI. SAP then sends an email with subject "PO: 789 Vendor CompanyZZZ.

It works fine for several cases and for other cases, it gets another Vendor.

I have searched the internet and the SDN forum to try and understand why I am having this error. I couldn't find any clue to help me solve this issue. I am working under ECC 6.0 and this is the configuration that is actually working for PO Titles:

- Output Type NEU and on processing routines have a new entry - medium 5

- Using standard program i.e. SAPFM06P, FORM routine is always ENTRY_NEU and custom form YYMEDRUCK_NEU

- Then in PARTNER FUNCTION I have an entry: medium - 5 and function - VN

- For subject of the mail in Mail Title and Texts I have --> PO number &EKKO-EBELN& Vendor &LFA1-NAME1&

- Under General data -> Replacement of text symbols, program is SAPMM06E and Form Routine is

TEXT_SYMBOL_REPLACE

- Vendor's Email are maintained as well.

- Communication Methodt is CS01 with the Cover Page Text value --> PO number &EKKO-EBELN& Vendor &LFA1-NAME1&

Have any of you got a clue where may I look to try and see what is going on?

Thanks a million.

Regards

Ernesto