sort differs on Mac and Ubuntu

On Mac
$ echo -e "bed,B\nbedatco,B" | sort -t , -k1
bed,B
bedatco,B

On Ubuntu
$ echo -e "bed,B\nbedatco,B" | sort -t , -k1
bedatco,B
bed,B

Both are
$ sort --version
sort (GNU coreutils) 8.22