Well that is extremely embarrassing, can’t believe it went unnoticed for so long.
Best regards and thank you all for your time and patience.
Edit: A question remains; out of curiosity, why did it work properly when installed as a temporary addon?
possibly because that used the windows file system to resolve the file, which ignores the case of files.
I was assuming the same, I guess the fact that it worked that way made me even more oblivious to the casing difference.
Thank you, again, for the help with the matter.