... but actually it's not possible to link them when we press Save button. This behavior misleads the users.
FYI: RO templates are missing at the "Configuration -> Templates" page.

They are available on editing a host or on mass update action.
According to the current rules that templates require RW rights to be linked, they have to be hidden from selection it they have only RO rights.

I'd suggest to hide RO templates from selection if we not going to allow such linkage.

Highly connected issue ZBX-3534