Binary executable file with write permission get READONLY from vim

Question

First I know that use vim to write a binary executable program is not recommended. So, I don't want to talk about its rationality here.

I have a binary program, with permission 755(owner is root), so as user root, I expect the fact that I can write to it. The program is not running, with command lsof and fuser, no output return, then I open it with vi, and type :wq to just write and quit, then vi warns me that E45: 'readonly' option is set (add ! to override). The problem is who set the readonly option? The linux kernel?

Then I add a !, which is :wq! now, the program cannot run now, which is expected.

And the same file with the same permission on another machine with the same OS and kernel version. This time, I can write to it with :wq, the magic here is that I can run the program at this machine, though the md5sum gives different results.

The system is RHEL 6.4. vi in fact is vim.

EDIT: add some command output as @ctrl-alt-delor suggested.

[root@localhost x]# uname -r
2.6.32-431.29.2.2.ky3.1.x86_64
[root@localhost x]# whoami 
root
[root@localhost x]# lsof XXX 
[root@localhost x]# fuser XXX 
[root@localhost x]# ls -l XXX 
-rwxr-xr-x. 1 root root 5178556 Apr 19 13:27 XXX
[root@localhost x]# ls -la
total 5080
drwxr-xr-x.  5 root root    4096 Apr 21 19:23 .
drwxr-xr-x. 10 root root    4096 May 18  2018 ..
-rwxr-xr-x.  1 root root 5178556 Apr 19 13:27 XXX
drwxr-xr-x.  5 root root    4096 Apr 18 17:24 blabla
drwxr-xr-x.  2 root root    4096 Apr 15 18:59 blabla2
drwxr-xr-x.  8 root root    4096 Apr 22 10:36 blabla3

EDIT: according to @Wildcard's comment.

[root@localhost x]# getfacl XXX 
# file: XXX
# owner: root
# group: root
user::rwx
group::r-x
other::r-x

[root@localhost x]# lsattr XXX 
-------------e- XXX

EDIT: add SELINUX info

[root@localhost x]# getenforce 
Permissive
[root@localhost x]# cat /etc/selinux/config 

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
SELINUX=permissive
# SELINUXTYPE= can take one of these two values:
#     targeted - Targeted processes are protected,
#     mls - Multi Level Security protection.
SELINUXTYPE=targeted 

[root@localhost x]# ls -Z XXX 
-rwxr-xr-x. root root unconfined_u:object_r:usr_t:s0   XXX

Answer 1

Rewards should be given to @Murray Jensen.

The short answer is the ~/.vimrc make the difference.

On the machine that I can't save with :wq:

[root@localhost x]# cat ~/.vimrc 
set fileencodings=utf-8,gb18030,ucs-bom,cp936

vim will check utf-8 validity, if illegal byte found, set the readonly option. It won't set the readonly option in binary mode.

After commenting this line, I can save the file with :wq now.