Hello Americo330,
I am sorry to hear about your paper tray not closing properly on your Officejet 8600. On my OJ 8600, the paper tray will not close fully if the extender for "legal size" is extended. There is a blue tab that you can hold in as you push the tray closed to release the extender, you will see it as you look down into the tray on the left side. This worked for me, please let me know if this works for you.
Thanks!:)