Signature will not change when selecting different account from dropdown menu

When sending a new email, the default email/signature is whatever email is highlighted in the inbox. I used to be able to click the dropdown menu at the top of the 'new email' window, select a different account and my signature would change to whichever email account I selected. Outlook no longer does this and I have to manually redo my signature each time I send an email or highlight a message from my inbox from the account I wish to send from. Is there a setting I can change to fix this? What needs to be tweaked to make it automatically change again? Please help.