Unwanted code appearing when compiling to plain text file

Would appreciate your help with the following. I’m using Scriv to write my drafts and then compile and export them afterwards. I’ve been compiling my Scrivener files as plain text documents and then copying and pasting into my wordpress posts. Problem is I get a lot of unwanted code embeded into the document
and I have to spend time removing it. Is their a better way to do this.?

Appreciate any advice.

This is, from what I understand, a known bug with some browsers (Safari included) and the TinyMCE editor plug-in that WordPress uses—it will happen no matter where you paste the text from, even a plain-text editor. Try using Firefox instead.