Missing icons in admin bar

I just updated my version of WordPress to 3.3. After updating, I’ve encountered a somewhat annoying problem. When logged onto my WP site the admin bar hovers at the top, as normal, but its icons are missing – the WordPress W, the update arrows, the pluss sign…

When accessing the dashboard, the icons on the bar appear as they should, but as soon as I go back the the site itself, the icons disappear again. I’ve tried to clear the browser cache, and I’ve tried the re-install button, but to no avail.

Does anyone have any suggestions as to what the problem could be?