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 .