With the test case, it show b - with gnu, it shows bde:

export C=./target/debug/coreutils
echo abcde > in
echo "bde" > ref
($C dd skip=1 count=1 bs=1; $C dd skip=1 bs=1) < in > out 2> /dev/null 
diff -u ref out

comment the first line to come back on GNU

To run it:
bash util/run-gnu-test.sh tests/dd/not-rewound.sh