What all solutions above at least implicitly discussed was the need to preserve $/ for the next round in the outer while{} loop. That's why all solutions use at least one local statement to keep the old value of $/.

You should take some time to study the solutions and next time maybe be more explicit at what dosen't work with your program, as the program works almost well (except for one warning on undefinded data). I guess a more representative dataset would have been

XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXaaaa
abcdefghijklm%nopqrstuvw%xyz
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
XXXXXXXXXXXXaaaa
abcdefghijklm%nopqrstuvw%xyz
[download]

which dosen't work that well with your original program.