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.

<hr><i>drh added on 2010-02-10 13:20:00:</i><br>
The &#91; and &#93; characters are also legal for Unix filenames.  (Any character 
other than 0x00 and / is valid in a unix filename.)  But &#91; and &#93; are used
as globbing characters by the shell, so there use must be escaped in the shell.
this can lead to subtle problems.  So as a safety mechanism, I deliberately
disallow such filename characters in Fossil.

Behavior is by design.