Problem with D800 in wireless i-TTL

Have to exchange now the second YN568EX (Nikon version) having the following problem:
In wireless iTTL mode, the flash fires with my D800 NOT. All things described below was able to confirm with his D800 an acquaintance, so it also was not due to my camera:

Scenario 1: wireless i-TTL (off-camera flash), flash is set to remote display with "Sn", group A, channel 1, mode "i-TTL". The built-in flash of the D800 is set to "Master", integr. Flash on "-" Group A "TTL", group B on "-", channel 1. When the camera triggering flashes of integr. Lightning, and also the Yongnuo sends a weak preflash, but after that nothing happens, the main flash will not fire, picture is dark, the audible signal of the Yongnuo also remains out although the audible device icon in the LCD is active.

Scenario 2: as above, but now group thus set in the camera A to "M" manually, eg 1/4: here even more remarkable, the Yongnuo shows after triggering the camera now indeed correct "1/4" in the LCD on, So has the information from integr. Flash of the camera get, but emits no lightning, also no acoust. Signal.

Scenario 3: This we have found only after long try by chance: if we set the camera in Group A and Group B on "TTL", then the Yongnuo suddenly works correctly, at least about 8 out of 10 times. Incidentally, then regardless of whether the Yongnuo is set to A or B.

Scenario 4: When the camera's internal flash as a master with Group A on "TTL", group B on "-" stands and mirror lock-up is activated, regardless of whether 1,2,3 seconds, then flashes the Yongnuo roughly 8 out of 10 correct.

This perhaps indicates a timing issue so that the Yongnuo only works correctly if between the master flash of the camera and the trigger is a certain delay as described in 3) just by activating the group B can occur (it will then be more information from the master flash the camera sent to it will be tripped).