I think what I’m going to need from you is a very simple self-contained example that reproduces the behavior you’re seeing, because I haven’t been able to get anything like it to happen (and no reports from any other serial users either).
Something like a project with one window, a couple buttons, very very clear what it does, e.g. “press configure, press read, go to terminal and write ‘wwwwwww’, watch as the wrong result comes in”.