join bug?

[Erez PERELMAN]

hey, i think there is a bug in join command.  i'm joining two sorted files 
and there is no joining for an expected mapping. here is the example:

f1:
79 53

f2:
791 834
79 82

join f1 f2 == blank

if i change f2 to:
1791 834
79 82

join f1 f2 == 79 53 82

thanks,
erez