cygwim comm command

I am finding unexpected and seemingly inconsistent results with the comm command.  It seems to work as expected with a pair of two-line text files, i.e.

file1:

fcomm
f1



file2:

fcomm
f2


but with larger files (15-20 lines)  I cannot consistently pick out the unique or common lines.

I am running CYGWIN_NT-4.0 LS136 1.3.12(0.54/3/2) according to uname.

Are there any known bugs with this command?

Thanks

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