mcfunction files with uppercase letter in file name cannot be executed

*.mcfunction files with uppercase letters in their file name (e.g. testFunction, Testfunction)cannot be run with the function command. Names with all lowercase letter and/or underscores (e.g. test_function) work fine.

Attempt to run the foremetioned function produces error "Expected whitespace to end one argument, but found trailing data at position x etc."

to reproduce:

1. create any datapack with a function with uppercase letter in file name.
2. reload and run the function with same name in game