Interestingly perldebug, under the heading Calling the debugger, lists four valid ways to call the debugger - and none of them use the #! line. So I guess that using #! to invoke the -d option is not valid..

To be fair though, perlrun says: you still can get consistent switch behavior regardless of how Perl was invoked, so we have some inconsistency in the doc. Although a lawyer might argue that the switch behavior is consistent - it is the underlying effect of the switch that is not.