Is that also normal behaviour of a grand?
That it easy to verify. I'd recommend to make an appointment with your local piano shop and test the B5 on a few accoustic pianos...
The other possibility would be, to consult with a piano teacher right at your digital piano for an hour or two.
Listening through headphones is the _first_ thing in the diagnostic chain. If the answer is:
. . . "B5 sounds the same as other notes, through headphones",
a lot of other stuff is ruled out.
If the B5 sounds different than adjacent notes _through headphones_, :
. . . It could be a problem in the CA78's samples, . _All_ CA78's will have that problem.
. . . . . I haven't read that other owners are unhappy
. . . with that particular note.
. . . It could be a problem with the B5 key's velocity sensor. I think the CA78 uses optical sensors, which makes the problem
. . . . . unlikely, but possible. In that case, a visit by a tech might be worthwhile.
If it's a "velocity problem" on the B5 key, it might be fixable with the Virtual Technician.
If the B5 sounds different _through the CA78 loudspeakers_:
. . . There might be a "room resonance" problem, unique to the DevNoteHQ's room and piano position.
. . . . Move the DP to a different location in the room, and see if things change.
. . . There might be a resonance in the CA78 "cabinet + loudspeaker" system. Again, I haven't read that it's a problem
. . . . . for other owners.
My bet is, if he _does_ go a piano showroom and play several acoustics, he'll find that _most of them_ have one or more notes that have a slightly different tone quality from the adjacent notes:
. . . but it will be different notes on different pianos!
Even brand-new "wood, felt, and steel" pianos have peculiarities, as they come out of the factory.
My suggestion -- FWIW -- is that, since DevNoteHQ has bought a premium DP from a good maker, he should leave it in "default condition", and get used to it for a few weeks or so.
. . . _Then_, start playing around with the Virtual Technician.