Re^2: mysteries of regex substring matching

[LanX]

> reading the last capture with embedded Perl code like /(....(?{print $1})){4}/

demo: (using /x for clarification)

  DB<66> $x = q[AAD34017837201D98AAED18778DEF993];

  DB<67> $x =~ m/(?: (....) (?{say $1}) ) {4} /x
AAD3
4017
8372
01D9

  DB<68>

update

I think this explains your "mystery", they all match but only the last one is kept in $1.