CURRENT: UEFI boot does not work on ASrock Z77 M4

I'm utilizing two systems running FreeBSD Current (most recent) on top of
Asrock Z77 M4pro main PCBs (one is the uATX version, the other regular ATX). The
firmware is the last one a customer can pick up from Asrock's website and it is
dated from 2013. Apart from the fact that the hardware is not useful for any
reliable system, I'm out of resources to exchange these systems with more modern
hardware.

The problem I face is with UEFI. Both boxes do have their OS on SSD (Samsung
850Pro and Samsung 830). I've created a EFI partition of 800k in size with
gpart and it is the first one on the SSD. Both SSDs are UFS and GPT. The
partiton starts at block 40.
Such a configuration works with the very same SSD fine with more modern
hardware (checked with a Fujitsu Celsius M740/UEFI). But the crap Asrock
rejects to boot UEFI. I tried to prepare a hdd the same way - no success. 

The funny part is that any USB thumbdrive with UEFI boot only is booting UEFI
as expected and several Windows 8 or Windows 10 DVDs seem to have no problem.

Maybe the location of the EFI partition (starting block) keeps the secret to
success, but I failed to put the partition at a proper starting point. On the
other hand, all SSDs I have prepared so far for UEFI booting, start their efi
partition with block 40 and they boot.

The big question is: what is the efford to fix this issue - if their will be a
fixing ever? The firmware of those boxes is really as minimal as possible
regarding to options for UEFI booting - but it is fancy coloured ;-)

Many thanks in advance,

Oliver