I tested V10.3.2412 on Mac and PC just now when pasting in between emails and “its not a bug”. Its by design and you just “press the space bar” as i said and continue on and its gone.
I see too @Gary also advised previously to “just continue on typing” in his post in the other thread link above you posted. So that’s all you need to do. Works fine for me personally.
However if you don’t want to do that, then there is a Sleekplan request below to remove the paste options in Settings which you can vote for below.