Interesting, I'm also running 5.6.1 (ActiveState build 626), but I get different output:

Enter regex: a
Enter string: abc
Matches!
Enter regex: d
Enter string: abc
Enter regex: d
Enter string: abcd
Matches!
Enter regex: \d
Enter string: 3
Matches!
[download]

So maybe I understood the /o modifier correctly after all. Now I just need to know why it ain't working! Thoughts, anyone?

-Peter