On OS X, I verified that the problem existed in Perl 5.8.0 and 5.8.1, and was fixed in 5.8.2.
Here are the relevant parts of the 5.8.2 changelog, and the P5P messages:

http://www.nntp.perl.org/group/perl.perl5.porters/2003/10/msg84468.html

From: Slaven Rezic
Date: October 31, 2003 04:24
Subject: [PATCH] Off-by-one error in regcomp.c
In regexp error messages, file and line are not printed due to
an off-by-one error in regcomp.c. This patch fixes the problem

--snip--

--- regcomp.c.orig    2003-10-31 13:07:52.000000000 +0100
+++ regcomp.c    2003-10-31 13:08:07.000000000 +0100
@@ -5045,7 +5045,7 @@ S_re_croak2(pTHX_ const char* pat1,const
     if (l1 > 512)
     l1 = 512;
     Copy(message, buf, l1 , char);
-    buf[l1] = '\0';            /* Overwrite \n */
+    buf[l1-1] = '\0';          /* Overwrite \n */
     Perl_croak(aTHX_ "%s", buf);
 }
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--snip--
http://www.nntp.perl.org/group/perl.perl5.porters/2003/10/msg84501.html

Thanks, applied as change #21591.

http://search.cpan.org/src/NWCLARK/perl-5.8.2/Changes

[ 21606] By: nicholas                       on 2003/11/01  14:58:31
        Log: Integrate:
             [ 21591]
             Subject: [PATCH] Off-by-one error in regcomp.c
             From: Slaven Rezic <slaven@rezic.de>
             Date: Fri, 31 Oct 2003 12:16:11 +0000
             Message-Id: <1067602571.12768@devpc01.iconmobile.de>
             
             [ 21593]
             Test nit ; goes with change 21591
     Branch: maint-5.8/perl
      !> regcomp.c t/lib/warnings/regcomp t/op/regmesg.t
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