I am unable to get show-trailing-whitespace to work. Here is a test I did,

emacs -q foo.txt 

In Emacs I typed these commands,

M-: (setq show-trailing-whitespace t) RET M-: (setq-default show-trailing-whitespace t) RET 

Then typed 3 lines in the .txt buffer where every line contains a trailing whitespace. The trailing whitespaces do not get highlighted.

I also checked C-h o trailing-whitespace RET and it shows that this face is set to black foreground on red background. Still I don't see the trailing spaces highlighted in this manner.

What is going on and how to fix it?