Hmm...interesting.
So now that I'm aware of this symptom, and can readily replicate it, I spent a little more time learning about the Samba aspects.
As best as I can tell the pertaining section of the smb.conf file is:
...
case sensitive = auto
default case = lower
preserve case = yes
short preserve case = yes
...
I specifically have these under the [global] group, which means that the same settings apply to all the shares.
I have been able to determine that my Win 7/10 shares behave as expected: the case is preserved when a NEW file is created. It is only my NAS box that does not.
However, further on I discovered that in a CLI window the actual file object does in fact have the correct lower/upper-case, only the WPS folder listing shows the filename in ALL CAPS.
Further still...once a re-boot happens the WPS itself switches to show the correct mix of upper/lower-case, which is a perfect sync with what I see in the CLI itself.
Alright...so I'm running XWP here (1.0.14 - Oct_2021), not sure if that is causing this behaviour, however it is VERY weird that after a re-boot what XWP shows is correct.
Re: smb.conf settings, to rule out any of the above combinations as causing this behaviour I tried multiple combinations, including completely commenting these out. Turns out this had no impact.
What is interesting is that my Win 7/10 shares are flagged as supporting EAs, while the NAS box does NOT, so maybe that has some bearing on the outcome as well?