I've compiled Transmission 2.61 from source for my Xubuntu system.
I would like to know why some torrents are flagged as "blocked" randomly and what is the meaning of this behavior.
Thanks you

Is just a bad translation, in English it looks like this:Partage vers 0 de 0 pair connecté Bloqué
The word "stalled" is very difficult to translate to other languages without loosing the meaning. As can be seen in your screenshot, one torrent not active for a short time is "Inactif", the others not active for a longer time are "Bloqué"; the translator had to choose words for {idle, stalled} which is not easy, in Spanish I use more than one word: {sin cambio, inactivo} (which is "w/o change", and "inactive").Seeding to 0 of 0 connected peers - Stalled