There appear to be some existing minor UI bugs related to this designer already, but I found one related specifically to IE 11. I feel for you having to support IE at all, but I think 11 is still supported for Octopus. More details are here:
Let me know what your preferred method for submitting issues is. I can’t imaging piggy backing on another issue in Github is ideal, but do you want us to create a new issues there or always submit here first? Thanks!
Hi,
Thanks for getting in touch, and for bringing this to our attention in detail. I’m sorry you’ve hit this issue! I’ve been able to reproduce this as you’ve described and shown in your comment on that GitHub issue.
I’ve let the team that is handling this issue know about it, and we can leave your comment there. We do prefer questions and reports like this to be brought either here on this forum, or emailed to support at octopus dot com, as we don’t actively monitor GitHub comments. We can then raise the issue and let our team know about it right away. I appreciate you letting us know here so we’re aware. 
I’m sorry again about this issue. Don’t hesitate to reach out if you have any further questions or concerns.
Best regards,
Kenny