Trueline completely overwrite PROMPT_COMMAND, while it is already set to something necessary for VTE. I think a better way to set the prompt command would be to add the trueline command to the ones in PROMPT_COMMAND already instead of overwriting them
PROMPT_COMMAND="_trueline_prompt_command; ${PROMPT_COMMAND}"
Trueline completely overwrite PROMPT_COMMAND, while it is already set to something necessary for VTE. I think a better way to set the prompt command would be to add the trueline command to the ones in PROMPT_COMMAND already instead of overwriting them
PROMPT_COMMAND="_trueline_prompt_command; ${PROMPT_COMMAND}"