Hi Torok,
seems like no-one has answered your question.

IBO actually does refresh the row - and since it doesn't exist anymore, it
disappears. The refresh is done by looking for the identifier, but since
you've changed this on the server (which IBO has no way of knowing) the
server returns nothing!

To do what you (probably) want, change your trigger to something like
ACTIVE BEFORE INSERT POSITION 0
if (new.pcode is null) then
NEW.P_CODE = GEN_ID(GEN_PARTNER,1)

and set GeneratorLinks on your query.

HTH,
Set