Created attachment 2128 notification area screenshot I'm not sure if this would be considered a bug with UIM or with Xfce, but in Xfce-4.4.3 this wasn't an issues so I'm filing it here first. uim-toolbar-gtk-systray isn't allowed enough space on the notification area to display properly. It seems like the toolbar takes up roughly three icons worth of space be is only give one icon worth of space and thus the issue. I've attached a screenshot of my notification area showing the issue. I'm currently using 4.6RC1 from gentoo's xfce-dev overlay. Please let me know if there's any other information I should provide.
I also see this bug in XFCE 4.6.1 on FreeBSD/amd64 9.0-CURRENT. Pretty hard to discern which mode Anthy is in if all you have is a bunch of one-pixel-wide bars :). It used to work in 4.4.
Should be fixed in ad5a85c (xfce4-panel-4.7.7 once released) please reopen if the bug is still reproducible with this panel.
Snapshots for testing: http://foo-projects.org/~nick/packages/xfce4-panel-4.7.6git-c37dd16.tar.bz2 or wait for xfce4-panel-4.7.7.