Your segfaults are probably related to the bug I noted in Segfaulty. Namely, the for loop is iterating over the aliased values of @l, which you are deleting during the course of the loop. Not very nice :)

Thus it works at 43 chars, if you do:

perl -e'print splice@l,rand@l,1for@m=@l=<>' t.txt
[download]

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print