This was an issue in a few firmwares, but it certainly wasn't random, what it was , was this.
If you printed 1 sided it would print on the wrong side of letterhead/labels, if you printed duplex all was right with the world (Or vice - versa, I honestly can't remember which)
No matter, grab this tool here, and run it, then grab this firmware and extract it, point the tool at the firmware and the printer IP and do the update.
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for posts that resolve your issues. Your feedback counts!Joe Arseneau