..with my peers:
in all of my four downloading transfers there is the same peer but he always times out connecting so that i can't see which client he uses. And he even uses the same port like me!  Is this pure coincidence, a program-bug, a stalker or something worse(virus/hacker) going on?
I'm using Ubuntu-Linux(64bit) with Tixati v2.53 (64bit).
If i recall correctly this is not the first time ever that such thing happened to me
(the first time was in windows7 with a way older version of tixati).

Thanks for your time.

PS: and a big thank you to the devs of Tixati for creating such a great, versatile tool!

Are you sure its not you own IP (or your VPN/Proxies IP if using one), most likely scenario without any further info is its you own client, but you router dosnt support NAT Loopback (Most dont) thus it times out, when you connect to yourself because your router does support NAT Loopback you would see "Self Connect"

I am sure it is your own IP, actually you and yourself alone - the tracker collects the IP, port, client ... of every peer on the specific torrent. Tixati gets the peer list from the tracker and also lists your IP and port as a peer. Try to enable the column "source" to know where the peer is coming from!