Occasionally I receive e-mails with words, such as URLs, which are longer than the usual 80 or so characters. (Often these messages are also very long vertically.) When I view such a message in Evolution, the viewer scrolls right. If I scroll left while the message is still rendering, it scrolls right again. I would expect to see the leftmost part of such messages at the end of the rendering process, since English reads left-to-right. Scrolling right should only be done manually. evolution-2.12.3-1.fc8
I cannot reproduce this consistently, furthermore, it did to me only once. When I started to investigate it more, it started to act as expected. I suspect that some part of the code changed horizontal scroll bar position beyond the document's limit, so GtkHtml thought you have scrolled to the right already, but too much to the right, so it decided to correct it to maximal right for the rendered document. Which is the right thing in case you did move to the right by hand, not by program itself. As I said above, I cannot reproduce it again, maybe some race condition or something, in GtkHtml probably (I suspect gtk_html_private_calc_scrollbars).
Also, just to make sure this isn't another case of Caret Mode malfunctioning, check whether View -> Caret Mode is enabled.
Caret mode is disabled; I've never used it.
Moving this upstream. Please see [1] for further updates. [1] http://bugzilla.gnome.org/show_bug.cgi?id=522837