While editing an issue's description, toggling to preview and back shrinks the textarea

Summary

When editing an issue description on a new or existing issue and toggling from the "write" to "preview" and back to "write" the text area shrinks to awkwardly small height.

Steps to reproduce

Go to https://gitlab.com/gitlab-com/marketing/issues/591/edit click "edit" click "preview" on the description, click "write". Tested on Mac 10.11.6 Chrome Version 54.0.2840.71 (64-bit)

Expected behavior

The height of the textarea should be the same as it was before previewing.

Actual behavior

The height is awkwardly small.

Relevant logs and/or screenshots