I don't know the answer but 5.8.4 and 5.8.8 seem okay. On Fedora 6:

$ perl asdf.pl
Sequence (?T...) not recognized in regex; marked by <-- HERE in m/(?T 
+<-- HERE he Purl Caretakers' John)/ at asdf line 8.
$ perl -v

This is perl, v5.8.8 built for i386-linux-thread-multi
[download]

On Slackware 10.0:

[chad@thepurplebuffalo ~]$ perl asdf
Sequence (?T...) not recognized in regex; marked by <-- HERE in m/(?T 
+<-- HERE he Purl Caretakers' John)/ at asdf line 8.
[chad@thepurplebuffalo ~]$ perl -v

This is perl, v5.8.4 built for i486-linux
[download]