Hmmm,... Don't know how the KDE desktop components of LinuxMCE are configured,... But it's possible that the desktop KDE, and what LinuxMCE uses are stored in two different places,... In other words, it's possible that the KDE screens you are seeing is something like a switch user as opposed to just loading the previously suppressed full desktop with the same user authority that LinuxMCE is running at... where it would be using the same KDE settings, in desktop and normal modes.
Of course, the alternative is that the Orbiter setups are using the wrong DPI or font size for the stuff that's not pre-rendered. But Dianemo diverges from a normal LinuxMCE, doing something custom on the UI front, doesn't it??
Keep in mind that Ubuntu & Kubuntu are different in the font display arena. Earlier versions of Kubuntu had trouble with Intel graphics chips, while the Gnome based Ubuntu of the same version did just fine. There was something about the way KDE did its font rendering as it related to i915 chipset family compatibility.
If you are saying that a normal Ubuntu (Gnome-based) installation differs from a KDE installation of the same version, then that is expected. It was only KDE, and I think XFCE that were plagued by this problem. Gnome handled the Intel graphics chipsets fine.