Hello Dremwolf.
I understand your concerns with your Officejet 8600 Plus. I realize you are using several programs to print envelopes, but since you listed Microsoft Publisher, I will provided steps to try and resolve this issue.
I will provide a website from Microsoft listing some troubleshooting for Microsoft Publisher. Please click here.
If you look at the picture example, you will see a setting at the bottom that states "Feed". Make sure this is selected to center so it picks up your envelopes. Also, in "options", make sure you are selecting the right size for your A2 envelopes.
Try less envelopes, if you are placing 30 stacks of A2, then try 15 envelopes instead.
Please reference this HP document on Loading Envelopes In the Paper Tray.
If these steps don't resolve your issue, then please let me know.