Zoho reverts to font size 12 even when the default is set to 11

Zoho reverts to font size 12 even when the default is set to 11

It's just simply annoying. I want it to be 11, the default settings allow me 11, therefore I want 11 font. Every time I create a new mail, or reply to an existing, it switches to 12. Why? Please could you fix?