Composer inserts additional reply nesting when formatting response as 'Preformatted'

[andrew.jeffery]

$ lsb_release -rd
Description: Ubuntu 17.04
Release: 17.04

$ apt-cache policy evolution
evolution:
  Installed: 3.22.6-1ubuntu1
  Candidate: 3.22.6-1ubuntu1
  Version table:
 *** 3.22.6-1ubuntu1 500
        500 http://mirror.aarnet.edu.au/pub/ubuntu/archive zesty/universe amd64 Packages
        100 /var/lib/dpkg/status

To reproduce:

1. Hit reply to some mail to enter the composer
2. Use text-mode reply
3. Select the entire message
4. Change formatting from 'Normal' to 'Preformatted'
5. Observe seemingly random and unexpected reply nesting

I primarily run into this when replying to patches on mailing lists, but I don't think the problem is limited to such messages. I'll upload before/after screenshots to illustrate.