This has nothing to do with formulafill. The issue can be demonstrated with a very simple formula.
"ouϪ" contains "oü"
This formula should be false, but if you try it out in the Formula Workshop, it returns true.
I think this is because of the intricacies of Unicode, and the fact that the contains operator is case insensitive. Panorama uses an Apple API to check whether one string is contained in another, and it appears that this API gets confused by diacriticals if the Ϫ character is used as a separator. If I used Ώ instead, it worked ok.
If you really want to use the Ϫ character, you have options. You could use matchexact and wildcards, this works fine (returns false).
"ouϪ" matchexact "*oü*"
I think the best solution is to use the arraycontains( function.
That’s tricky. I’ll take Jim’s earlier advice and use data arrays.
I’d previously avoided them because my arrays are created using arrayselectedbuild so I have to create text arrays and then convert them to data arrays but that’s not a big deal.