Every bit of code has cost. 
Maybe Plex will make a change, but it’s so obviously a Roku bug that it’s hard not to suggest pressuring them.
Yeah. The Plex Transcoder is derived from FFmpeg. But if you replace it with a baseline ffmpeg a variety of things don’t work.
Some folks have created wrappers around the Plex Transcoder, but I think that would be more difficult here. I don’t think ffmpeg exposes any knobs to control behavior of these headers.
A wrapper could race to modify the remux’d temporary files before the client got them. Probably doable, kinda gross.
Easier to bug Roku. 
