I received a bonus like that at a job once. I stayed there about a month after that. They were upset when I left.

Your bosses will get away with as much as you let them. The 70 hour weeks are on you, but you can certainly approach them to understand why they are giving you that amount. You can explain it away by saying that you'd like to understand where you can further improve. It is, after all, a reflection of your performance.

If you can separate your emotions from the money, just ride it out for a year and get back that $20k you lost by switching to a RoR developer role at another company.