Weird problem with color depending on the exported mp4 dimensions

[Falrinth]

I have noticed someone having that problem on AE localised FB group and decided to test for myself, and indeed there is some issue here. I have created simple compositions with just a shape coloured red. TO be precise its #D71414

I have then duplicated the composition so one is 512x512 and other is 640x640. WHen i export it as H264 mp4 the one with dimensions 512x512 gets its colour changed. WHen i have tested QuickTime mov the color remains true on both dimensions. If i then convert mov into mp4 without touching After Effects, color gets switched again on the 512x512 composition. Is there a way to prevent it on smaller videos that must be mp4?

[Falrinth]

It seems Media Encoder is struggling with it for some reason, but free software like HandBrake converts the 512x512 mov into mp4 keeping its colour true: