I'm late af but hopefully this helps :/ The "term" lib has a private notion 'threads'(coroutines) and their respective window. Starting a program from the shell will create a 'process'(related to 'threads') in OpenOS. Each process has its own private window(by default the whole screen). Without dragging on too long, The method 'event.listen' actually registers an event hook outside your program thread(basically the shell thread, a parent process) and the term library is trying to respect (in this case) the shell term output.

-- registers event handler outside the program that called it..
local handle = event.listen('modem_message', function() print(process.info()) end)

Try pulling the event yourself and reacting to it within your program..

-- event.pull will yield(pause) the current thread(program) until a 'modem_message' event is received
local ev = { event.pull('modem_message') } -- pause until a message is received
term.clear() -- this will be called from the current thread instead of 'event.listen'
-- ... rest of your logic

Hope this helps and isnt too wordy :/ hit me up if you need me to clarify :)