Deleted field in custom form not deleted from database

I thing there is bug in customize form .
i want to update contact form but i get bellow error :
“email_id_2 field cannot be set as unique in tabContact,as there are non-unique existing values

I delete email_id_2 long time ago and it’s not there any more .
but still show this error .
Some one know how can solve it , Hope this problem will solve soon .

Fields are not deleted as a design. You might have to drop the column manually before uploading your data.

can you please explain more , i don’t understand .
in screen shot i send field deleted , i don’t have email_id_2 any more in form .

You will have to delete it from your database too…

Thanks so much @rmehta for your reply