The 1.8.489 update is an improvement, but there's still issues. If TTS volume is muted when you start the client, then raising the volume will do nothing (except other volumes will be reduced when something should be read out loud). If TTS volume is 1 to 10 when the client is started, then the TTS volume will remain at that level and cannot be changed (but it can be muted).

Thanks for the report.