new vim version in 20.04 sets mouse=a by default

[Christian Ehrhardt ]

Upgrading vim in Focal from 2:8.1.0875-5ubuntu4 to 2:8.1.2269-1ubuntu1 changed the default behavior.

Old:
:set mouse
 mouse=

New:
:set mouse
 mouse=a

That new behavior prevents most peoples common
In fact that is one thing that always annoys me when working with a Debian VM/Container to have switch to mouse=v to get things working again.

Issues:
- marking something with the mouse does NOT copy it anymore
- marking something with the mouse does not even allow right-click to copy
- probably more

Yes I know one could press shift to get the old behavior, but that isn't how the rest of the terminal works. I'd much prefer to "press shift for the uncommon/new behavior".

We always had in the changelog:
     - debian/patches/ubuntu-mouse-off.patch:
       + Mouse mode is actively harmful in some chroots.
Old bug 1661691 brought that delta in early 2017

But this was dropped on the last merge:
    * Dropped changes, included upstream:
      - debian/patches/ubuntu-mouse-off.patch:
        + Mouse mode is actively harmful in some chroots.
Yet if this would be upstream then the behavior would not have changed right?

Was this change intentional and is there a good reason that makes up for the drawback?
Or is it a bug that was missed on the merge of the new version and should be resolved before 20.04 goes into FF?

[Christian Ehrhardt  (paelzer)]

Subscribing Steve who did the merge according to the Changelog