Thanks Yenthe for a quick response. Yes I have enabled the mandatory answer checkbox. I am quit new in Odoo so i will need to check regarding the  source  code. I have created a new survey and I have the same problems. I couldn't reproduce this issue in runbot environment. 

Hi Limor,

For question one: did you enable the option to make it a mandatory answer? For example:

For question two: I've just tested this on the latest Odoo 11 and it seems to work fine out of the box. Is your Odoo source code running on the latest version? There have been quite some fixes in the last months for Odoo 11. Please update your Odoo source code. If you can still reproduce it then please try to reproduce it on an official Odoo test instance at runbot.odoo.com. If you can still simulate it there then please make a bug report at https://github.com/odoo/odoo/issues/new and Odoo will look at it as soon as possible.

Regards,
Yenthe