Bug or Feature in join?

[Ulf Lorenz]

Hello,

I admit I haven't searched the bug database, just came across the 
following problem with join version 5.97.

Two files, A and B. B contains all numbers from 1 to, e.g., 12.

a) A contains the two lines
        1
        10

   The output of join is _only_ the line "1".

b) A contains the three lines:
        1
        9
        10
   Now the output is correct (i.e., the lines "1", "9", and "10")

Now I wonder, is this a bug or a feature? And if so, how do I turn it off?


Ulf