Engine power and bleed pressure should be unrelated. The system diagrams I have show that initially bleed air pressure is regulated by an HPRSOV (LP air is unregulated on supply) and an Engine Bleed Valve. This air is supplied, in very small quantities, to pressurise the aircraft's water system. The next valve is the Flow Control Valve that regulates the pressure of the air supplied to the packs. My experience shows that typically pressure stays in the low 50's but some aircraft have the occasional tendency to rapidly fluctuate between 15 and 70 psi for no reason. The latter is permanently sorted out by a visit to hospital but can normally be corrected in flight by turning on the anti-icing for a few minutes.
Poorly functioning equipment is an unfortunate fact of aircraft operations. When it happens it gets put in the Tech. log and the techies sort it out. In Embaer's case, repetitive problems like this are normally fixed by a software upgrade and handled by your Engineers working in concert with the manufacturer's support team. After all, that is what you pay them for.
PM