psql behavior change on upgrade from version 12.x to 13.1

Using a MacBook Pro with the current Big Sur—Version 11.2 (20D64).

I just upgraded to PostgreSQL 13.1. (Earlier, I was on 12.x.) Using psql, the behavior of ordinary copy-and-paste has
changedramatically, and for the worse,  w.r.t. Version 12. 

HAS ANYBODY ELSE SEEN WHAT I REPORT BELOW?

First observation

Now, when I copy a single line SQL command, terminated with semicolon and newline from the Text Edit app (with
Command-Cor the menu item) and then paste it into psql (with Command-V or the menu item), the newline isn't respected.
Ihave to hit the return key by hand to see the effect. Moreover, the pasted line has a highlighted background. 

Second observation

When I copy _several_ lines of SQL commands from the Text Edit app and then paste them into psql, none of the newlines
arerespected. (I still get the strange highlight.) Now when I hit the return key, I get errors like this: 

  \i: extra argument "<the text of the line>" ignored

for every single line.

This makes a standard working practice that my fingers have learned over decades suddenly completely unusable.

NOTE: the \i metacommand still works as it always did.