What is the risk of leaving the MAN START PB 'ON' on the A320? During a manual start on a A320, the ENG MAN START P/B opens the start valve which then runs the starter motor. During the MAN START process, at some point, the start valve closes automatically. What are the risks associated with continuing to leave the MAN START P/B ON at this point?
Well, documentation is a bit vague about this, and I suppose a technician would know more about the different things the ENG MAN START bp is doing, but from a quick glance at the FCOM there is one major difference that I can spot:


  [The FADEC durring a manual start]  (...) Closes the engine start valve, and cuts off the ignition when N2 reaches 43 %.


Bold emphasis is mine, no other conditions except N2>43%.

Leaving the ENG MAN START pb on means FADEC keeps assuming we are trying a manual start, and will cut off ignition anytime the N2 is above 43%. No prob as long as engines are running, right?

But that means (I assume) when you then enter turbulent/stormy weather in flight and turn on  IGN/START to prevent a flameout, nothing happens as FADEC is happy that N2 is above 43% and you manual start has been ‘succesfull’.

I don’t really know if it will even attempt an auto restart when you get a flameout, as the N2 will probably keep windmilling for some time depending on your airspeed, so you could end up with a big problem.