Analyzing the peer-id format in the announce made by Tixati you can see that the random characters after the peer-id client coding is in a different representation depending on the, default or non, value of the client encoding.

Thus:

1. in case of the default TIX0253- the following random characters are represented normal like TIX0253-d7g6f7c0d9j5, both in the torrent event log and the captured announce packet, as oposed to:

2. Changing the peer-id client code to anything else, the random characters are still a random string of readable characters in the tracker event log but a percent encoded string in the announce packet, like -TR1111-d7g6%E5%23%C6%BAI%5B%CF%BF. The peer id length must be of 20 as stated by the BitTorrent protocol, that is not the case anymore.

I couldn't find a modality to proper change the peer-id, from Tixati options or directly editing the tracker, still having a proper length of random character string attached, generated by Tixati. I tried older versions but the issue remain.

Changing all the peer-id string, as like -TR1111-d7g6f7c0d9j5, works but the randomness disappear.

Am I missing something or it's just an unintended result of a good intention?

I've tried different other clients and all of them announce a NON URL encoded random string in the peerid.
Tixati does this only for the default id TIXvers-.
As long as one change the id to anything else, the random peer id Tixati generated string will be percent encoded. By doing this the whole changing peerid functionality is lost.
Why is that, anyone knows?