Epic tree form keeps content when adding issue/epic

Summary

(Summarize the bug encountered concisely)

Steps to reproduce

• enable epic_trees feature flag (#10795 (closed))
• click Add an epic
• enter text
• click Add an issue

Example Project

not on gitlab.com yet

What is the current bug behavior?

Text remains in input field:

Screen_Recording_2019-09-19_at_14.06.42

What is the expected correct behavior?

Input field is cleared when switching between adding issues and epics.

Possible fixes

Use two instances of the form component for issues and epics.