Move existing instance removal from init to render

If the instance isn't set to append, other instances on the target element should first be removed/torn down.

I don't foresee any issues with moving this, and all the tests are happy. I'd like to get another set of eyes and cerebral cortices on it, though.

Fixes #1430
I don't have any trouble reading this, but my fingers just don't seem to want type it automatically.