Calling wordwrap like this:
$sequence = "aaadaaadaaadaaada";
$sequence = wordwrap( $sequence, 4, "\n",1);

The \n is inserted correctly at the first position (just after pos 3), but is off by +1 for the remaining inserts.

Sequence becomes:
aaad
aaada
aadaa
ada

Where it should be:
aaad
aaad
aaad
aaad
a