Hello Adrian,
maybe one of the installed source files lead
to a bad gschemas.compiled file?
Could you create a file with the md5sums of all
the xml files that seem to get combined into that
gschemas.compiled file.
md5sum /usr/share/glib-2.0/schemas/* > ~/usr-share-glib-2.0-schemas-md5sums.txt
Also you may attach the gschemas.compiled too?
Kind regards,
Bernhard