org-edit-src-exit randomizes / mixes up code in source-buffer on exit

[mcg]

Hello,

org-edit-src-exit suddenly completely destroys my code after coming back 
from vacation. No known recent changes in configuration. Very strange 
error!

EXAMPLE: here a simple code before editing

#+BEGIN_SRC R

mtcars

sum(mtcars$mpg, na.rm = TRUE)

mean(mtcars$disp)

#+END_SRC

I enter to edit (org-edit-special), change the order of two lines and 
add a number:

Result I should get in source buffer after exiting:

#+BEGIN_SRC R

mtcars

mean(mtcars$disp)

123456789

sum(mtcars$mpg, na.rm = TRUE)

#+END_SRC

What I get in source buffer on org-edit-src-exit: (no joke!)

#+BEGIN_SRC R
rmtcars
s
ean(m
sums$di(p)mt123456789

cars$mpg, na.rm = TRUE)

mean

#+END_SRC


Came back from vacation and suddenly this happens. Only updates to 
server, elpa / melpa has not been updated the last three weeks. Emacs 
reinstallation did not help, launching without

Emacs 26.1 build 2 (2021-01-31) modified by debian

org version 9.4.6