Look at the 2nd level list in http://moodle.org/mod/forum/discuss.php?d=78322#p746293.

The HTML source says <ol type="a"><li>try to, the WYSIWYG editor shows a., b. according with the settings but... viewing the post together with the others breaks the type attribute settings. Guessing the theme is resposible for that.

See also MDL-25888: not sure but maybe of any help even here.

TIA,
Matteo