Comment 2 for bug 109931

Well, it looks like that did affect it, according to a
  http://en.wikipedia.org/wiki/Bash#In-process_regular_expressions

Basically, the single quotes surrounding the regex become part of the regex. So the above code becomes:

  if [[ "foo.tex" =~ ^(.*)\.tex$ ]]
    then
      file=${BASH_REMATCH[1]}
      echo "File is: $file"
    else
      echo "Not a TeX file"
  fi

That's a pretty significant change. A lot of scripts will be broken. More warning should have been given to users about this.