Command-line parameters lost to Perl

I run Indigo Perl under Windows XP. My problem is that Perl scripts
aren't able to see the command line that invoked them, unless I
prefix their name with an explicit call to my Perl interpreter.
Why not?

For example, I have a simple script listargs.pl which counts and
lists its command-line parameters (in array @ARGV).

If I invoke:
listargs.pl a b c
then I get:
0 parameters

However, if I invoke
perl listargs.pl a b c
then I get:
3 parameters:
a
b
c
as desired.

Can anyone suggest why the command-line parameters are lost in the
first form?

- Rich