This has been tested under windows only.

Create a file named: $ () + ,-!= @ [ ]^_{ }~.txt

This file is perfectly legal under windows (WinXP) but if i try to add it via:
fossil add "testCase-fileUpload\$ () + ,-!= @ [ ]^_{ }~.txt"

I get

fossil: filename contains illegal characters: testCase-fileUpload/$ (
) + ,-!= @ [ ]^_{ }~.txt

Basically it chokes over the  ] and [ characters.

Regards.