The square brackets cause the svn permissions manager to think a new section has been encountered, which causes a lot of extraneous, non-existent directories to be listed in the svn authz file and shown in the UI (and possibly thrown at FE/Cru, but I haven't verified that).

I'm not sure what happens with spaces, but anecdotal evidence suggests group names with spaces may play havok also.

Known possible solutions are:
1) Fix repoman to work with these
2) Prevent non alphaNumericHyphenUnderscore groups from being created, upgrade the names of existing such groups, and remove any such lines from the svn repository authz file.

The only known workaround at the moment is to avoid using groups with square brackets in their names.