Tax code at service Level

Hello Gurus,

I have configured to maintain the tax code at service level (ML100), now I want to set this field mandatory, I have done the configuration for this behavior. But When making the service PO, whithout maintining the tax code field it's letting me save the document and it's not being showed in the service lines screen (in another system it's showing). The only way the system ask me to fill this field is if I double click in the service line and I go to Tax tab.

It's strange because in another clientes I can see the field in the main service line screen.

Have you ever had this kind of problem?

Regards,

JM