Yup, the problem was with unpack indeed... I changed the line below from:

my ( $ino, $off, $len, $name ) = unpack( "LLSZ*", $buf );
[download]

To:

my ( $ino, $off, $len, $name ) = unpack( "L!L!SZ*", $buf );
[download]

And the program finally worked as expected:

[me@localhost ~]$ ./test2.pl -d sample/ | head
sample/xaaaaaaaaff
sample/xaaaaaaabdu
sample/xaaaaaaabjw
sample/xaaaaaaaaos
sample/xaaaaaaaalu
sample/xaaaaaaaags
sample/xaaaaaaabci
sample/xaaaaaaabhy
sample/xaaaaaaabjv
sample/xaaaaaaaaxa
[download]

All good, but some questions remains:

1. What could have happened that cause this change in the system? Originally I didn't need to worry about that. Maybe some change related going from 32 to 64 bits platforms?
2. How can I double check if I need to use "native" sizes with the unpack template? Besides the program malfunctions, of course. :-)