I have done further tests in the last hours. The password can successfully be set if it is 7 characters or less. Even though it explicily mentions that the password must be 2-8 characters if a longer password is entered, an 8 characted password is SILENTLY IGNORED and nothing is set.
A shorter password works. My guess is that either only complete morons are left in Intels BIOS department or that Intel got a letter from the NSA telling them to make their crappy 8 char security even MORE crappy.
And please remember, this is all on a mainboard that is advertised by Intel as: