Yeah, orbital mechanics gets a little bit mind-bendy sometimes. If you're in a stable circular orbit, accelerating in the direction you're traveling will actually result in you traveling more slowly because you have moved to a higher orbit, and firing engines to slow down will actually speed you up because you move in closer to the host body and take up a faster orbit.

This is actually a problem spacecraft deal with regularly. If a Dragon capsule is behind the ISS and wants to dock, using its thrusters to accelerate toward the ISS will actually result in it falling further behind. Decelerating will get it closer, though it will then be in a lower orbit. Orbital rendezvous is tough.