TESTFIELD Message differs in NAV CSide and RTC (Web Service)

Hello All,

I just have found that, error messages for TESTFIELD function differs in C-Side and for RTC (Web-Services).

In OnOpenForm trigger of Form 42 "Sales Order" and Page 42 "Sales Order", I added one Statement like,

TESTFIELD("Document Type", "Document Type"::Order);

The error message on running
Form,
Document Type must be Order in Purchase Header Document Type='Quote',No.='ER/MT/0490'.
and in Page
Field Document Type in table Purchase Header must be equal to 'Order'. Current value is 'Quote'.

Why it differs?