I'm not sure there's a way to do so. It may simply be a function of the SMF 1.x software. I've checked a few other SMF's of that version and it's giving me the same issue.
SMF 2, however, seems to have fixed the issue, but it's in release candidate stage, and while I'm all for having release candidate and betas on my own computer, I don't really want to inflict that upon the site.
When SMF 2 comes out, I will upgrade it pronto, but I haven't found a method to change it now, because it's all embedded in the forum's software.
EDIT: Did some more research. It may be possible for me to adjust the tab sequence. Maybe.