On master remove your calligrathumbnail.desktop from the installation

[Friedrich W. H. Kossebau]

Two more notes:

Yes, there are no thumbnails created for xfig and wmf files yet, because the 
kdelibs thumbnail system just picks the first in the list of thumbnail 
creators which claim support for a type, and sadly the plain image thumbnail 
creator coming with kde-runtime does that for both types, even if it cannot, 
and that creator is first in the list by accident.

Fixed only for 4.8.5 and 4.9 (by removing that claim). You can fix that 
yourself locally by editing the 
$(GLOBAL_INSTALL)/share/kde4/services/imagethumbnail.desktop and removing 
image/x-xfig and image/x-wmf there.

And yes, thumbnails done by the Sheets part are broken. I have not yet managed 
to create a fix for that, due to the different scaling/zooming approach there. 
Anyone with expertise in sheet rendering code is welcome to kick that in shape 
or tell me how to do it (using the zoomhandler seems not sufficient).

Cheers
Friedrich