This started after the last update to version 15.4 (fedora 20).
1. login and receive several hundred feeds dating back to several years ago.
2. mark them all as read so that they go away. (as an aside, sometimes the counter on the system tray icon does not match the actual program, so I have to right click the icon and mark all read there as well).
3. Application will work as normal after this until I quit the program and restart it, in which case you repeat the process starting at step 1.