I've had problems on a tracker with "Invalid event= from client".
According to viewtopic.php?f=4&t=7117 this is a problem that happens when the tracker doesn't know how Transmission handles partial seeding.
Unfortunately, just knowing this doesn't help--I know what causes the problem but there's nothing I can do about it.
Could you please add an option to Transmission that lets the user turn off this behavior and does what it would otherwise normally do for partial torrents? (I could hack it myself to take this out but I wouldn't know what normal behavior to put in instead.) It's still listed as a draft extension and not standardized yet, so some trackers don't have it.