If you are having the problem while scanning directly from the control panel then no software is being involved. The scanner would be relying entirely on the firmware to create and send the document to the destination. You could look into a firmware update if there are any newer versions available.
Are we talking about Scan to Email, Scan to Network Folder or Scanning directly to a PC (via USB) in this scenario? Is the problem only with scanning documents to PDF? If so you might want to test scanning to .Tiff and compare. We want to make sure we are talking about the right scenario.
It also would be a good idea to contact HP and see if you have any warranty options remaining on your printer. Since this is a fairly easy to reproduce problem that does not necessarily involve scanning software its a good candidate for HP phone support. See what they have to say and post back to us any findings.