I recently upgraded vim on Arch Linux which broke syntax highlighting of 
certain shell scripts. An example of such script:

    #!/bin/sh
    foo=$(cmd --arg)
    echo "$foo"

With 7.3.834-1, the syntax highlighting was fine. Since 7.3.875-1, the syntax 
highlighting was broken. Try it yourself:

    vim -u /dev/null +'syntax on' foo.sh

I bisected (git-remote-hg :-) ) it to:

    Author: Bram Moolenaar <bram@vim.org>
    Date: Tue Mar 19 11:35:58 2013 +0100

    Update runtime files.

This is a diff of the change to runtime/syntax/sh.vim
@@ -1,9 +1,10 @@
 shArithmetic
 shDeref
 shDerefSimple
+shEcho
 shEscape
 shNumber
-shOperator
+shOption
 shPosnParm
 shExSingleQuote
 shSingleQuote
@@ -16,4 +17,4 @@
 shTest
 shCtrlSeq
 shSpecial
-shCmdParenRegio
+shCmdParenRegion

shOption causes the invalid syntax highlighting here. The attached patch makes 
the `--` option stop at the closing parenthese too (seriously, who uses `--)`) 
anyway? It is a syntax error). Applied on top of 3.7.875, current workaround is 
to copy the file from /usr/share/vim/vim73/syntax/sh.vim into 
~/.vim/syntax/sh.vim and apply the patch.

Originally reported at https://bugs.archlinux.org/task/34523

Note, these changes somehow do not show up in the patches on ftp. Also, it 
stopped halfway applying due to 
https://groups.google.com/forum/#!topic/vim_dev/atNg4a30770