User Exit DLL does not restrict system from saving data.

I have an User Exit DLL on tfacp200. I have added some simple business logic which is executing properly. Even though system sets an error message in the execution and returns dalhookerror, data is getting saved in the session.

I have tried below simple code to re-check:
function extern long ue.before.before.save.object(long mode)
{
on case mode
case DAL_NEW:
break
case DAL_UPDATE:
dal.set.error.message("gbacp300.03")
return(DALHOOKERROR)
endcase
return(0)
}

Even this does not restrict system from updating record.
Please help.

Thank You in advance!!