Getting nuts! simple onSubmit process but does not work...

Question

hello.
once again my little problem:
on page 1 i have a report. every row has a link:
http://192.168.255.20:7777/pls/htmldb/f?p=116:21:3135390112602440240:END_TASK:::END_ID:22
where END_ID:22 gives the id of the row to a textfield on page 21 which is launched.
on page 21 there is a small "report" of only the chosen row to give us again the details of the chosen row.
there are additionally 2 buttons, button END_ID which stores the id that we've got through the link's URL, and another textfield P21_AUFTRAGSDAUER i can enter some stuff into.
and there's a submit button that submits the page (NO redirection or something like that).
now on the same page 21 i created an onSubmit process which should update the chosen row. it's launched after all verifications and stuff, and its source is
update wartungs_auftraege
set status=2,
time_spent = :P21_AUFTRAGSDAUER
where auftrags_id = :END_ID
and now there's the strange thing: while in
time_spent = :P21_AUFTRAGSDAUER
the placeholer :P21_AUFTRAGSDAUER is replaced correctly with the entered value, :END_ID in
where auftrags_id = :END_ID
is ALWAYS replaced with 1, although it shows the correct value that was passed through the link's URL! i just don't get it anymore! i've taken a look at the source code, and both inputs look the same:
<INPUT TYPE="text" NAME="p_t01" SIZE="30" MAXLENGTH="2000" VALUE="22" id="END_ID" >
<INPUT TYPE="text" NAME="p_t02" SIZE="30" MAXLENGTH="2000" VALUE="21" id="P21_WARTUNGSDAUER" >
i'm getting nuts with that, i'm trying since 2 hours to solve this problem... :(((
please help me, anyone! thanks...

Answer 1

the END_ID item was created by using the create-element-wizard. its source type is set to (i try to translate it from german)
used alternative source: only if current value of session is NULL
source type: ITEM (application or site element name)
source value:
END_ID
standard value:
&END_ID.