[O] problem with html export of links

[Johannes Brauer]

Hi!

I have two files.

 a.org contains the anchor defined by custom_id property

* headline
  :PROPERTIES:
  :CUSTOM_ID: anchor
  :END:

and

b.org contains the link to a headline in a.org with custom id #anchor

[[file:a.org::#anchor]]

Clicking the link in b.org all works fine. But exporting b.org to html I get 

…
  b.org contains the link to a headline in a.org with custom id #anchor
  </p>

  <p>
  <a href="a.html#MissingReference">a.html#MissingReference</a>
  </p>
...
with #MissingReference instead of #anchor. I cannot figure out, what the 
failure is.

Johannes