Re: M-w, then C-y. C-y inserts text properties that aren't on original.

[MON KEY]

,----
| The root cause of this mess is the confusion in text properties.
| Text properties (as opposed to overlays) become part of the text
| they're applied to, yet they're mostly used (e.g. for font locking)
| in situations where they're not intrinsically part of the text.
`----

The ``moslty'' generalization is far too broad a stroke.
You seem to be reducing this to a matter of presentation.

,----
| It would be better if these uses could use overlays, then copying
| the string would ignore the overlay.
`----

No, it would not.

There are a good many uses (some as yet poorly explored) where text
properties are the more suitable ``container'' than the equivalent
approach with overlays.

If anything it would be better if overlays were further deprecated.

/s_P\