bug#38908: Bug on comm or sort

[Saint Michael]

I am trying to use the comm utility to compare two list of IP addresses,
sorted with regular sort (not -n), and the result is erroneous. I could not
find the answer in Google.

list1=
208.78.161.18
208.78.161.19
208.78.161.20
208.78.161.206
208.78.161.207
208.78.161.21
208.78.161.22
208.78.161.224
208.78.161.226
208.78.161.227

list2
208.78.161.17
208.78.161.18
208.78.161.19
208.78.161.20
208.78.161.206
208.78.161.207
208.78.161.21
208.78.161.22
208.78.161.224
208.78.161.226
This command should work
 comm -12 --check-order <(sort list1.txt) <(sort  list2.txt)
my environment
export LC_ALL=C
export LANG=en_US.UTF-8
export LC_CTYPE="en_US.UTF-8"
export LC_COLLATE=C

why these lists are no being compared correctly?