The logic around those switches is a bit broken and inconsistent.
The -a switch should be renamed -xa.
Use of any -x* switches should trigger exactly ONE export dump. (The current -x/-xr behavior is stupid, because the "work" module is of course part of the root scope; no point in dumping that again.)
Any combination of -x* switches missing -xr should imply dumping the "work" module only.
Oh, and where did the help text for the -a switch go?
The logic around those switches is a bit broken and inconsistent.