Debian bug #231229.
In that bug, it has been analysed that while swat behave correctly by proposing "default case" only on a share basis, the documentation (at least the smb.conf man page) suggests that it can be set globally (just like other name mangling options).
Peter Eisentraut confirmed with a glance at the code that the option is not registered as a global option (which is also confirmed by running testparm on a smb.conf file wontaining it in the global section).
So, unless the option should be allowed as a global option (and thus, this bug would turn out to be a bug in the code), the documentaiton should probably be fixed.
- John T.