Bitmap from related table not showed in NAV2013

Hello, on page 46 (Sales Order Subform) I added a field with source AISMagStatus.Picture, where AISMagStatus is a table different from page source table (Sales Line).

To bind data from Sales Line to Status table I added this code that manage a Semaphore related to logistic status

IF Location.GET(“Location Code”) THEN BEGIN

IF Location.“Gestito AISMag” THEN
BEGIN

IF “Completely Shipped” = TRUE THEN
Semaforo := 5
ELSE
Semaforo := AISMagFun.NewSalesOrderLineReady (Rec);
END
ELSE
BEGIN
Semaforo := -1;
END;
END;

AISMagStatus.GET(Semaforo);
AISMagStatus.CALCFIELDS(Picture);

where Semaforo is integer and unique key of AISMagStatus and Picture is a BLOB with subtype Bitmap.

But nothing is rendered.

Instead if I fill a new bitmap field added to Sales Line

“AISMag Status” := AISMagStatus.Picture;

and I expose this new field, the bitmap is rendered correctly.

Any idea?