Gutenberg: Regression: Weird behavior with default appender, appears to create two blocks

[jasmussen]

There are a couple of issues present in master that were not in 3.1.

1. Click the default appender ("write your story") in Chrome, notice how there's a weird flickering
2. Try in Firefox, note how an empty block is created.
3. Try clicking below the appender, which should rediret the click to the appender — it appears two .blocks are created _until you move the mouse_.

See videos of issues 1 and 2 here.

GIF of issue 3:

Compare with the behavior in 3.1:

[jasmussen]

CC @mcsf because he originally noticed this issue in https://wordpress.slack.com/archives/C02QB2JS7/p1530722631000171?thread_ts=1530722631.000171&cid=C02QB2JS7

[aduth]

Taking a look.

[aduth]

Looking like #7699 may be a culprit here.