No, the display being blank at low voltage is the powerfail interrupt kicking in too - this is the same software fix as the other power problem.

It's not necessarily very low voltage, but there is a dip in the (empeg's) local power when the display filament heater starts up, as this takes 250ma @ 5v and this can, in low voltage (less than about 12.2v) trigger the powerfail interrupt - which, as a matter of course, blanks the display...

You may have problems measuring the voltage drop when the starter is running as most multimeters have long sample periods - a storage scope is probably required.

Hugo