Created attachment 193531 [details]
Sample document showing the effect

I think this is a bug, because it results in poor usability, and it's counter-intuitive:

Consider you have a text document with
(default-styled text)(e.g. bold text)

Now if you mark all text in the line and paste it at the end of the line, what happens?

You do *not* get this:
(default-styled text)(e.g. bold text)(default-styled text)(e.g. bold text)

But instead you get:
(default-styled text)(e.g. bold text)(bold text)(e.g. bold text)

That is the style at the end of the line (at the cursor) is not "canceled" when inserting unstyled text, but the attributes are "continued".

Usually when pasting text, the text is pasted *with* attributes (unless you use special paste), but that's not happening here, or at least not as expected.

In contrast when you start with
(e.g. bold text)(default-styled text)

And repeat the experiment, you get (the expected)
(e.g. bold text)(default-styled text)(e.g. bold text)(default-styled text)

because the style at the cursor (end of line) is *not* "continued".

See the sample document.