Client ID spoofing is not really an issue, as the tracker doesn't identify the user by that. And they had the client accepted, so it was not necessary to spoof on their site.
Is there really a new ratio cheating problem with Tixati?
some details why they think it can be used for cheating ratios?
Every torrent client can be used for cheating easily without modification. And even if you have no clue how the protocol works and how to game it, a simple "how to cheat bittorrent" search will lead to something like RatioGhost.
The ban likely just means that Tixati was the preferred client of the person(people) who blatantly cheated and got caught. It's correlation, not causation.
Cheaters gonna cheat. Some trackers just think banning based on this torrent client results in an acceptable amount of collateral damage.