Trying to print 6.5x3.625 envelope but it keeps cutting off

[jrasicmark]

I have Word 2007 in Windows 7 and I'm trying to print on an HP Officejet 4500.
I've been asked to print on 6.5" wide x 3.625" envelopes.
I figured out how to add this custom size to my printer in my Windows control panel and I also added the custom size from within Word.
It worked great the first time I printed it, but every time I try printing more, the text and graphic shift farther to the left, getting cut off the edge of the envelope.
Windows and/or Word seem to automatically round the figure up from 3.625" to 4", but I don't understand why that should cause everything to shift to the left (and farther left each time I print).


Finally, I thought maybe I should only have re-set the custom size in Word, instead of both Word and the printer control panel.
So I changed the printer control panel back to letter sized and tried printing from Word again using my custom size.
It worked great! Then I tried printing another (they need 50 copies) and it was shifted back to the left off of the envelope again!
I originally created this document in InDesign, then exported it to a PDF and tried to print from the PDF, and when I had trouble printing from Acrobat, I re-saved the PDF in Word format from Acrobat.
I don't know what else to try!
Has anyone had a similar problem and know how to fix this?
I'm attaching a photo of my failed attempts just to show what I'm trying to describe.