When setting up a TT-RSS source, Liferea pulls continuous updates, downloading all of the feed data and then immediately downloading the data again. This cycle will continue until Liferea is closed, causing high load on the TT-RSS instance, and will immediately resume when Liferea is restarted. While this issue causes no noticable problems in Liferea's UI, if running TT-RSS on a small server it can cause enough server-side load to interfere with other webapps.
I see this behavior with both Liferea 1.8.7 and 1.8.10, both using TT-RSS 1.6.0 as a back end. However, this post from the liferea-devel mailing list seems to indicate that the issue has been present since at least Liferea 1.8.0 and TT-RSS 1.5.7: http://sourceforge.net/mailarchive/forum.php?thread_name=4F01473E.8060803%40exyr.org&forum_name=liferea-devel
A lightly sanitized log produced using liferea --debug-all is attached.