HP feeds extra sheet after job

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I can't figure how to solve this problem. I have an HP deskjet 6940 with an
added bottom tray where I use the upper tray for envelopes. Windows Vista
and Microsoft Office 2003.

After each and every printjob, from any program (Word, Notepad, Wordpad,
print test page, fax receipt, anything! Even printing a blank page) a print
command goes to the printer (per blinking light) and it prints another,
blank page from the top tray.

I've tried everything I can think of. All the preferences seem to be okay.
H-P support was not at all helpful. I installed the printer driver again.
I uninstalled printer and software and re-installed it. I uninstalled
Office Suite and reinstalled it.

Any solutions?

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