Sometimes it identifies it as malware, sometimes as a worm, sometimes as a trojan, always tixati.exe and always outbound. Did I maybe download something dodgy with Tixati or is Malwarebytes just getting it wrong?

If you downloaded the program from the Tixati website everything is fine.
Tixati has NO spyware or malware.

Has anyone else experienced this? Just so I know whether this is Malwarebytes misidentifying Tixati as malicious or whether I might not be downloading something actually malicious in Tixati.

In such cases you should follow up with MalwareBytes directly and ask them whether it was a false-positive.
I've tested it right now (MB Trial 4.4.4) with Tixati 2.84 - no matches, all clean. MB only detects BitTorrent (client) and uTorrent and FrostWire installers as Adware/Malware/PUP due to them bundling unwanted software.

If you used Tixati from an installer, the installer and .exe files are digitally signed (the dev paid a hefty sum for it!) - right click, properties, 'Digital Signature' must be for 'Tixati Software Inc.', sha256 currently. If there's no digital signature, the files must've been infected (modified) by other software.

If you use portable version then https://support.tixati.com/Release%20Verification
The dev does not provide file hashes (like md5, sha256) but they would be equally valid for verification if they came from a trusted source (still the key / signature method is better)

If the verification reveals an infected file, keep it as a sample.

if Malwarebytes is detecting outbound traffic I would Enable Tixati's IP Filter and add the IPs Malwarebytes into it, or exclude it from malwarebytes, your choice.

what's likely happening is that certain IPs in the swarms of torrents you downloaded/downloading are part of an IP range + port that is a combo for a "known threat". but given that bittorrent uses random ports.. it's chance that simple filters like that will catch a false alarm.