Kcollectd-0.9 includes a mime-type definition in /usr/share/mime/packages/kcollectd.xml According to the author, whom I have contacted to report an unrelated bug, this file should be enough to provide file association with the datafiles created by Kcollectd and become the default filter in Kcollectd's file selector: at the moment, neither these features are available. Reproducible: Always
Please sync in an hour and re-emerge kcollectd; this should be fixed then. (Added calls to re-build the desktop mime database after installation.)