I've been using https://stackoverflow.com/a/17761144/788700 to get multiple major modes in rst-mode. It has been working in Emacs 24.3. However as emacs develops the same code gradually stops working.
as I go from rst-mode chunk to py-mode chunk emacs switches the major mode.
In emacs-24.5 it doesn't work automatically anymore, but one can make emacs to switch mode locally by issuing new line:
(same behaviour in emacs-24.4)
In emacs-25.0.5 it doesn't work at all:
only syntax highlighting works, but modes doesn't switch as I go from one chunk to another.
Here's minimal configuration which reproduces the issue: