[15/11/2016 12:14:46 PM] Applied filter "[REDACTED]" to message from [EMAIL REDACTED] - [SUBJECT REDACTED] at 15/11/2016 12:14:27 PM forwarded

I am using Thunderbird 45.4.0. I have a few basic filters set-up to automatically forward emails to other people based either on subject line or from: address. What appears to be happening is Thunderbird correctly identifies these messages and runs the filter but does not properly forward them - instead a new empty draft email window pops up by itself each time a matching email is received. Checking my sent folder confirms that no email has been sent. For example, doing a test with one basic filter that has 'Subject contains: (phrase)', do the following: 1: Forward to someone@somewhere.com, 2: Mark as Read, 3: Move to Folder 'Archives', this will happen: I get an empty draft window as described and the message is marked as read and moved to the right folder. Checking the filter logs confirms this (excuse the confidential scrubbing here...) [15/11/2016 12:14:46 PM] Applied filter "[REDACTED]" to message from [EMAIL REDACTED] - [SUBJECT REDACTED] at 15/11/2016 12:14:27 PM forwarded [15/11/2016 12:14:47 PM] Applied filter "[REDACTED] -> to message from[EMAIL REDACTED] - [SUBJECT REDACTED] at 15/11/2016 12:14:27 PM marked as read [15/11/2016 12:14:47 PM] Applied filter [REDACTED] to message from [EMAIL REDACTED] - [SUBJECT REDACTED]Reminder at 15/11/2016 12:14:27 PM moved message id = 73675af2-060b-b361-9b02-4978b6bd3cf1@[REDACTED] to imap://[EMAIL REDACTED]/Archives I've searched for solutions to this but no one seems to have the same specific issue I do with the draft email windows instead of forwarded messages.