I get the same behaviour with 5.8.4, BTW. It seems that when the range 0..-1 is used to select the elements of the slice ($#rv is -1 when @rv is empty), the 'final element' of the slice (incorrectly) evaluates to the previous/last element on the Perl stack (or some such). With Perl versions up to at least 5.8.4, that is — but no longer with 5.8.8 and 5.10.0 (I currently don't have access to versions 5.8.5 - 5.8.7, so I can't tell when it got fixed).

(Ranges like [99..98] behave the same way as [0..-1], so what seems to matter is just that the second value in the range is smaller than the first...)

my @x = ('A','B');

print "-------------------\n";
print "[foo", scalar(@x[0..2]), "]\n";
print "-------------------\n";
print "[foo", scalar(@x[0..1]), "]\n";
print "-------------------\n";
print "[foo", scalar(@x[0..0]), "]\n";
print "-------------------\n";
print "[foo", scalar(@x[0..-1]), "]\n";
print "-------------------\n";
[download]

With 5.8.4 (and earlier), this prints

-------------------
Use of uninitialized value in print at ./663945.pl line 9.
[foo]
-------------------
[fooB]
-------------------
[fooA]
-------------------
[foo[foo]
-------------------
[download]

and with 5.8.8 or 5.10.0

-------------------
Use of uninitialized value in print at ./663945.pl line 9.
[foo]
-------------------
[fooB]
-------------------
[fooA]
-------------------
Use of uninitialized value in print at ./663945.pl line 15.
[foo]
-------------------
[download]

As has already been pointed out elsewhere in the thread, this is mostly expected behaviour, because (from perldoc -f scalar)

scalar EXPR
(...)
Because "scalar" is unary operator, if you accidentally use for EXPR a parenthesized list, this behaves as a scalar comma expression, evaluating all but the last element in void context and returning the final element evaluated in scalar context.

...except for the "[foo[foo]", of course.

I don't have a real explanation (probably simply a bug)...  just a couple of related observations with respect to using [0..-1] with slices. When you use a literal list instead of a named array, there's still some curious behaviour in recent releases of Perl:

print "-------------------\n";
print "[foo", scalar(('A','B')[0..2]), "]\n";
print "-------------------\n";
print "[foo", scalar(('A','B')[0..1]), "]\n";
print "-------------------\n";
print "[foo", scalar(('A','B')[0..0]), "]\n";
print "-------------------\n";
print "[foo", scalar(('A','B')[0..-1]), "]\n";
print "-------------------\n";
[download]

prints

-------------------
Use of uninitialized value in print at ./663945.pl line 26.
[foo]
-------------------
[fooB]
-------------------
[fooA]
-------------------
Argument "[foo" isn't numeric in list slice at ./663945.pl line 32.
[fooA]
-------------------
[download]

The '"[foo" isn't numeric...' seems to suggest that with [0..-1] the value "[foo" is being used to index the element from the list... which is confirmed by this:

print "-------------------\n";
print 2,  scalar(('A','B')[0..-1]), "]\n";  # elem at index 2 (undef)
print "-------------------\n";
print 1,  scalar(('A','B')[0..-1]), "]\n";  # elem at index 1 ('B')
print "-------------------\n";
print 0,  scalar(('A','B')[0..-1]), "]\n";  # elem at index 0 ('A')
print "-------------------\n";
print -1, scalar(('A','B')[0..-1]), "]\n";  # elem at index -1 (last e
+lem 'B')
print "-------------------\n";
print -2, scalar(('A','B')[0..-1]), "]\n";  # elem at index -2 ('A')
print "-------------------\n";
print -3, scalar(('A','B')[0..-1]), "]\n";  # elem at index -3 (undef)
print "-------------------\n";
[download]

which prints

-------------------
Use of uninitialized value in print at ./663945.pl line 37.
2]
-------------------
1B]
-------------------
0A]
-------------------
-1B]
-------------------
-2A]
-------------------
Use of uninitialized value in print at ./663945.pl line 47.
-3]
-------------------
[download]

Looks like this "indirect indexing" feature could be useful for obfus ;)