For what it's worth, I have an HP printer that, every now and then, farbles pdf's that people have sent me.  I've never had it do that to DBA things, though. I was told by an IT person that this can happen when the file does not compile properly before being sent to the printer, and that it often does it when the computer hasn't been turned fully off for a while to clear all buffers, etc. I have found that the instances of bizzaro-print are greatly reduced when, every now and then, I close all programs, turn the computer completely off for a few, and restart it. Hope this helps.
Ann Luce
EMI Filter Co.