Mail saves drafts even after email is sent

Using GMail IMap...

When cerating emails it saves a draft. I notice drafts are often there AFTER I send the email. Sometimes I have sent the draft to be told I sent the email twice. Not good.

If I change to save Drafts On My Mac I dont think I get this, but then I cant access my drafts on my other computers. So I have to save it as IMAP but then get this issue.