Why is “echo foo | read a ; echo $a” not working as expected?

Question

I could replicate the problem with various shells under FreeBSD, GNU/Linux, and Solaris. It had me head-scratching for more than an hour, so I decided to post the question here

Answer 1

Just FYI; in ksh it is working as expected; See also http://kornshell.com/doc/faq.html, Section III (shell programming questions), Q13:

Q13.    What is $bar after, echo foo | read bar?
A13.    The is foo.  ksh runs the last component of a pipeline
        in the current process.  Some shells run it as a subshell
        as if you had invoked it as  echo foo | (read bar).