When email pop out option is used to create email response, the main email window in the background should be closed!
This is fixed in latest Enate release 2019.2.
this is addressed and will be part of coming release.
logged by our operations team, similar to MS outlook when you pop out draft email the previous draft should be removed automatically from the email tab.
Currently user must cancel original draft if email was popped out which is an extra step.