Webkit does not render dropdown toggle for the calender in http://dilbert.com/fast. Two drop down toggles fail to render; the drop downs themselves are functional and selectable however. This bug is present in the GTK test browser built from the head revision I pulled from git on Sat, Jan 10 at 8:30 am (GMT -5). It is also present in 39572.
I don't see the problem with Mac OS X.
It works for me with current git master
Please feel free to re-open if the problem still occurs for you.