Originally reported downstream (the example screenshot is also attached there): http://bugs.gentoo.org/show_bug.cgi?id=348373 If the panel is gorizontal --- everything is OK. But if the digital (Digital! Analog displays correctly.) clock are displayed on (for example in my case) right-side panel, it's rotated +90 degrees (see the screenshot in downstream bugzilla). xfce-base/xfce4-panel-4.6.4 in the same case works as it should (displays correctly).
Made optional through hidden property "rotate-vertically" in 5056f2d. Will be made configurable in 4.10, see bug #7027.