This was on purpose to allow improperly coded KDE applications to show up, for instance synaptic will not work otherwise as it uses OnlyShowIn=KDE.
The problem is identified in bug report 1364.
I understand how this dual test was added after 3.5.10, when TDE was still considered KDE. Now that TDE is a recognized standalone XDG desktop, the dual testing for both TDE and KDE should be removed in R14.0.0.
I don't know that the change should be backported to 3.5.13.x, but the change is needed in R14.0.0.
Darrell