lock/unlock changes

I was trying to password protect a folder. I simply wanted the folder to be password protected, and I don't use it very often.
So, I tried setting permissions to "write only" for all users (including me), and it worked perfectly: it gave me an "access denied" message when I tried opening it.

However, if one clicks cmd+i, anyone can simply set the restriction to "read and write", without the master password being asked.

If I click on the lock, I need to type the password, but I can change settings anytime without clicking on the lock.

What's going on?