Steps to reproduce:
1. Make a forum post.
2. In the HTML editor, use the indent button to indent a paragraph
The indent is lost.
Looking, It seems that the HTML editor adds a <div style="margin-left: 40px;"> to do the indent, and Moodle then strips out the style attribute.
Also, if you try, as a work-round, using a more semantic <blockquote> tag, it seems that the Moodle 2.0 stylesheet sets that to 0 indent, which is stupid.