As nobody answer to may bug report since 2017-05-14 :
http://bugs.kde.org/show_bug.cgi?id=379818

I decide to post here.

Initial conditions :
- OS : Leap 42.2
- Kernel : 4.4.62-18.6-default - x86_64
- File system : ext4 and xfs
UUID=857c3295-5944-4593-82e2-bb90dede4312 / ext4 noatime,acl,user_xattr 1 1
UUID=6173a3df-4407-427c-b01a-c2d664471fc8 /data3_dwnld_pub xfs defaults 1 2
- ACL : 2.2.52-8.55
- KDE : Frameworks 5.26.0 - Qt 5.6.1 (built against 5.6.1)
- KATE : Version 16.08.2

Goal : In folders defined as "PUBLIC" for users in group "publicuser', any users can do anythings but cannot delete objects they do not own.

1st Step : Creation of initial group, user and folders
Create group publicuser
Create user publicuser (no login user), user_test1, user_test2
Add publicuser, user_test1, user_test2 to group publicuser
Create a new folder :
mkdir -p /d_pub_folder
chown publicuser:publicuser /d_pub_folder
Create sub-folder for each regular user
mkdir -p /d_pub_folder/user_test1
chown user_test1:publicuser /d_pub_folder/user_test1
mkdir -p /d_pub_folder/user_test2
chown user_test2:publicuser /d_pub_folder/user_test2
Set properties on new folders
chmod -R 770 /d_pub_folder
chmod -R g+s /d_pub_folder
chmod -R +t /d_pub_folder
Set ACL on new folders
#set user to rwx, group to ---, group publicuser to rwx,other to ---
setfacl -R -m u::rwx,g::---,g:publicuser:rwx,o:--- /d_pub_folder
#set default : user to rwx, group to ---, group publicuser to rwx,other to ---
setfacl -R -d -m u::rwx,g::---,g:publicuser:rwx,o:--- /d_pub_folder

2nd Step : Files creation
Create new files owned by each user in their respective folder
su to user_test1
echo "Create by user_test1 in user_test1's folder" > /d_pub_folder/user_test1/testfile_1.txt
su to user_test2
echo "Create by user_test2 in user_test2's folder" > /d_pub_folder/user_test2/testfile_2.txt
Create new files own by user_test2 in user_test2's folder
echo "Create by user_test2 in user_test1's folder" > /d_pub_folder/user_test1/testfile_4.txt

3rd Step : ACL Check from a "public" folder /d_pub_folder/....
1°) OK : any user can create a file in it's own folder
2°) OK : any user can create a file in folder owned by others
3°) OK : any user can modify a file they owned in folder owned by others
4°) OK : any user cannot delete a file they do not owned any where
5°) OK : any user can modify a file they do not owned using vi in a terminal emulator (Konsole)

What does not work
USING KATE or KWRITE
6°) FAILED : any user cannot modify a file they do not owned. Write is denied

PS : please see "Bug 379818 - Kate, Kwrite seems to not apply acls rules" for attachement and screenshots.

Any help is welcome.