Desktop Client doesnt show message when folder is read only

hello,
i have a shared folder and one user have “read only” permissions.
after the sync is completed and i can access the folder from windows explorer, i can read the content -> thats ok

when a “read only” user create a file or folder, so the file ist created and the sync log show:

grafik

my questions:
when i use dropbox and have the same settings (folder - user only read) so i recive a message when i will create a new file: you dont have the permission
and i cant create it.

on nextcloud, it doesnt show any message and my user think it the permissions doesnt work.

can anyone help?

NC Version: 12.0.1
Ubuntu: 16.04.3 LTS
Apache: 2.4.18
PHP: 7.0.18-0