I can't reproduce your problem with ActivePerl 5.6.1 build 635, but I can reproduce it with ActivePerl 5.6.0 build 623

>c:\progs\perl588\bin\perl 730963.pl
Line has 6 words. 'This is some space separated text'
2 3 4 5 - This-is-some-space-separated-text
Line has 4 words. 'On three different lines'
17 22 21 - On-three-different-lines
Line has 6 words. 'So you can see what happens'
2 3 4 5 - So-you-can-see-what-happens

>c:\progs\perl561\bin\perl 730963.pl
Line has 6 words. 'This is some space separated text'
2 3 4 5 - This-is-some-space-separated-text
Line has 4 words. 'On three different lines'
17 22 21 - On-three-different-lines
Line has 6 words. 'So you can see what happens'
2 3 4 5 - So-you-can-see-what-happens

>c:\progs\perl560\bin\perl 730963.pl
Line has 6 words. 'This is some space separated text'
Argument "1," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "2," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "3," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "4," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "5," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "6," isn't numeric in numeric eq (==) at !.pl line 25.
2, 3, 4, 5 - This-is-some-space-separated-text
Line has 4 words. 'On three different lines'
Argument "1," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "2," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "3," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "4," isn't numeric in numeric eq (==) at !.pl line 25.
17, 22, 21 - Argument "5," isn't numeric in numeric eq (==) at !.pl li
+ne 25.
Argument "6," isn't numeric in numeric eq (==) at !.pl line 25.
On-three-different-lines
Line has 6 words. 'So you can see what happens'
Argument "1," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "2," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "3," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "4," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "5," isn't numeric in numeric eq (==) at !.pl line 25.
Argument "6," isn't numeric in numeric eq (==) at !.pl line 25.
2, 3, 4, 5 - So-you-can-see-what-happens
[download]

The only workaround I've found is to change
my $regexp_p = qr/$PatternCore/;
to
my $regexp_p = $PatternCore;

And if you really want to have fun:
Try changing my $Regexp_ref;
To: our $Regexp_ref;

You mean $regexp_p? No change. my $regexp_p, our $regexp_p and local our $regexp_p all produced the same result.