Help! Dirty airbrush?

[QuackingPlums]

Only the second time I've used this airbrush on a car shell, and probably the only time I've used black. I had it apart and sitting overnight in airbrush cleaner and was sure that no black was coming out before I started on the other colours, so what is this effect? Did I somehow miss a part in my cleaning?!



I couldn't see that it had done this because I had the outside wrapped in cling film, and the creases were obscuring it... oddly only appears to have happened on one side too!

Also, notice how the black has obviously oversprayed onto the top of the side windows - I was holding the brush perpendicular to the roof at the time, so would I be correct in assuming I had the pressure up too high? What do I need to do next time to avoid this?

Luckily it's only a Mardave shell so I can afford another...