Well, I guess I spend about 15 minutes on your post. 15 minutes I could not use answering other questions - either here or on comp.lang.perl.misc. Testing, and then rejecting (but note you need to have decent knowledge to come up with the right test cases...) an offered solution not only takes time, it also decreases the overall percieved usefulness of this site, and the helpfulness of the community.
A question left unanswered gives only minimal damage. Wrong or incomplete answers are downright harmful.
As for Programming Perl, it writes:
If PATTERN is also omitted or is the literal space, " ", the function splits on whitespace, /\s+/, after skipping any leading whitespace.To me, that seems to indicate Programming Perl describes exactly the behaviour I mentioned.