Since liferea started using sqlite for storing the feed information, the beagle search engine is no longer capable of indexing them. There is a bug report about this in the gnome bugzilla, see http://bugzilla.gnome.org/show_bug.cgi?id=472934
The first comment to this report says:
"This will be hard to do ... its very hard, mostly impossible, to track changes in sqlite without app support."
Would it be possible to add such support to liferea?