Unless its old, that stuff shouldnt flake off. I would take it to the company that did it and show them. if there a decent company they should redo it.
I have heard that spilling gas on it will take it off. So, maybe some solvent like varsol or brake cleaner? As long as there's no clear coat on it. That might make it tough. If it is cleared might have to sand it off and repaint. I dunno, just some ideas.
I would say only if left for extend period of time, best suggestion would be to either do sections at a time and rinse or with a deagreasing soap and water or do the whole panel then wash off. either way just make sure you remove it thuroughly so it cant affect your panel.