Going from Germany to Hungary is easy: you just go. There are no border checks. You can cross over completely naked, if you like. Except, apparently, not on a bus.
It turns out the German gov't requires bus lines to knowexactly who is on their bus. But if the Russian embassy has your passport, you've no way of proving your identity. So you're not allowed on the bus. So you don't go to Hungary.
So you make a new plan. In the 2+ hours it takes you to get home from the bus station. But you can't write it down, because you don't own a pen. So hopefully you'll remember it tomorrow, and go out and buy some pens.