IE11 keyboard problems with issue templates

Summary

Customer is reporting keyboard issues when attempting to create a new issue using a template, in IE11. The problems occur only while first editing a new issue based on a template, before saving the issue. After saving the issue and editing again, everything behaves as expected.

https://gitlab.zendesk.com/agent/tickets/92464

Steps to reproduce

From the customer:

Applicable to Internet Explorer v11.2068.14393.0 (only version to which I have access)

Creating a new issue using a template, before it is initially saved, I have observed the following problems:

1. The up and down arrow keys do not move the cursor to the previous and next lines as expected. Left and right arrow keys work as expected. When I hit the up or down arrow keys the cursor remains in place. 
- Performing the same steps in Firefox, the cursor moves previous and next as expected. 
- Performing the same steps in IE, in an issue *NOT* created using a template, the cursor moves previous and next as expected. 
- Performing the same steps in IE in an issue created using a template but has already been saved, the cursor moves previous and next as expected.

2. The Enter key does not insert a new line as expected. When I hit the Enter key, random bits of text that I have previously changed revert to their original text and the cursor remains in place. 
- Same steps in Firefox, newline is inserted as expected. 
- Same steps in IE, in an issue not created using a template, newline is inserted as expected 
- Same steps in IE, in a templated issue already saved then edited, newline is inserted as expected.