bug#21190: cut runs wrong

[zsw]

I 'm a user of linux   today  I  find the  command    "cut"  runs wrong  , file 123 is :

1 2 3

4 5 6

7 8 9

after use the cut command :

$ cut -f1 123.txt

1 2 3

4 5 6

7 8 9

I  want to know where is wrong ,can you help me? thank you .