GNU Parallel Bug Reports First read of {} has strange behavior

[Zachary Vance]

parallel --version

GNU parallel 20140722

parallel has strange behavior with {} on occasion:

echo -e "a\nb\nc" | parallel -I {} -- bash -c "echo {} && echo {} && echo {}"

a

a

b

b

c

c

xargs does not:

echo -e "a\nb\nc" | xargs -I {} -- bash -c "echo {} && echo {} && echo {}"

a

a

a

b

b

b

c

c

c

Why is this happening? Is it a bug or just a difference of interface I'm not understanding?