V4 Alpha 6: Popover errors when using `hover` trigger

Created by: JD-Robbs

When "quickly" hovering over a list of Popovers (trigger = hover), the introduction of the isAnimating check is causing quite a few errors.

Here's a reproduction: https://jsfiddle.net/kzhszdpa/

Simply hover quickly (i.e. move the cursor fast) from the topmost button down and then up again and check the console output.

• Operating system and version: Windows 10
• Browser and version: Chrome v55

Similar issues appear with regards to Modal and when interactions are "too fast" (for lack of a better description) - albeit I have not found a way to re-produce this in a simple fiddle.

Edit: see #21607 (closed) for an issue that may be related.