That is curious indeed. I remember back in April when I started developing a complicated set of macros that depended on the use of local and instance variables I ran into problems with local variables seemingly persisting. After fiddling around (as every software developer does 
) I found the solution was to capitalise the word ‘local’ in my variable names leading me to think that case is significant.
A quick search of the forum made me ROFL: in this post from June 2020 Local & Instance Variables Still Show in "Preference:Variable" - #4 by tiffle
I specifically tell @martin that case doesn’t matter.
Well, as it says in my profile - “This is my most recent senior moment... that I can remember”