[O] Bug: HTML blocks in macros called before lists break in 7.5

[amscopub-mail]

Sample code:
-------------

#+MACRO: start #+BEGIN_HTML\n <mydiv> \n#+END_HTML
#+MACRO: end  #+BEGIN_HTML\n </mydiv> \n#+END_HTML

* Hello world

{{{start}}}
 1. Item 1
{{{end}}}

-------------------------------
Expected HTML export (valid HTML):
----------------------------------

<mydiv>
  <ol><li>Item 1</li></ol>
</mydiv>

-----------------------------------
Actual HTML export (invalid HTML):
-----------------------------------

<mydiv>
  <ol><li>Item 1</mydiv>
  </li></ol>

OK, so the example is a bit contrived. But that's basically the technique that 
I use to style lists. (It may not be the best but for complex START/END macros, 
using HTML blocks is the way to go.) 

Anyway, the above code worked fine in 7.4. Then I upgraded to 7.5 and I now 
have literally hundreds of these broken lists. 

Ideas? Where would the offending org code be?