What hippo said. It's quite easy to exemplify this effect:

c:\@Work\Perl>perl -wMstrict -le
"my $overwrite = qq{AAAAA\rbbbb\rCCC\rdd\rE};
 print $overwrite;
"
EdCbA
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Update: I would say the problem is likely not so much with leading or trailing carriage returns as with embedded  \r characters as in the example.