When converting a lead to an account, the custom mandatory fields in the account are not treated by zoho as mandatory

When converting a lead to an account, the custom mandatory fields in the account are not treated by zoho as mandatory

In my Account module I have a number of custom fields that I have set as mandatory. When I enter a new customer as a new account they work, I can't save the record without populating them.

However when I convert a lead, my CRM users are able to save the account without populating the "mandatory" fields.

How can I control this?