Or it was just faulty firmware and he did hit the (almost) correct conclusion:
ADEN bit on g4:
"Note: The software is allowed to set ADEN only when all bits of ADC_CR registers are 0 (ADCAL = 0, JADSTART = 0, ADSTART = 0, ADSTP = 0, ADDIS = 0 and ADEN = 0) except for bit ADVREGEN which must be 1 (and the software must have wait for the startup time of the voltage regulator"
No errata needed, it's clearly stated that you cannot just set ADEN without waiting for certain other conditions.