please assume following setup:

control/virtualdomains:
intellitest.at:intellitest

users/assign:
+intellitest-:qmdummy:900:900:/var/qmail/poboxes/intellitest-at:::

/var/qmail/poboxes/intellitest-at/.qmail-default:
./Maildir/

mails for whoever@intellitest.at are delivered smoothly into  /var/qmail/poboxes/intellitest-at/ Maildir - so far so good. 

Mailheader shows:
Delivered-To: intellitest-whoever@intellitest.at

the further we go the better it looks.

now i tried to insert X-Delivered-To into the mails by setting up .qmail-default. (thanks to Anand Buddhdev). but here the trouble starts. qmail-local ignores the .qmail-default. i deleted it and mails are delivered. i set up .qmail with some forwarding address it is ignored...
to put it in a nutshell: any .qmail[-default] is ignored.

what am i doing wrong?