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**Do you want to request a *feature* or report a *bug*?**

bug

**What is the current behavior?**

`onMouseEnter` is fired on `disabled` buttons.

**If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem. Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Paste the link to your JSFiddle (https://jsfiddle.net/Luktwrdm/) or CodeSandbox (https://codesandbox.io/s/new) example below:**

https://codesandbox.io/s/react-onmouseenter-on-disabled-buttons-fskwd

**What is the expected behavior?**

`onMouseEnter` shouldn't be triggered on `disabled` buttons.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

React 16.11.0 (not sure when it started to happen)
Chrome/MacOS

CHILD.click();
    expect(idCallOrder.length).toBe(2);
    expect(idCallOrder[0]).toBe(CHILD);
    expect(idCallOrder[1]).toBe(PARENT);
  });
  it('should stop after first dispatch if stopPropagation', () => {
    putListener(
      CHILD,
      ON_CLICK_KEY,
      recordIDAndStopPropagation.bind(null, CHILD),
    );
    putListener(PARENT, ON_CLICK_KEY, recordID.bind(null, PARENT));
    putListener(GRANDPARENT, ON_CLICK_KEY, recordID.bind(null, GRANDPARENT));
    CHILD.click();
    expect(idCallOrder.length).toBe(1);
    expect(idCallOrder[0]).toBe(CHILD);
  });
  it('should not stopPropagation if false is returned', () => {
    putListener(CHILD, ON_CLICK_KEY, recordIDAndReturnFalse.bind(null, CHILD));
    putListener(PARENT, ON_CLICK_KEY, recordID.bind(null, PARENT));
    putListener(GRANDPARENT, ON_CLICK_KEY, recordID.bind(null, GRANDPARENT));
    CHILD.click();
    expect(idCallOrder.length).toBe(3);
    expect(idCallOrder[0]).toBe(CHILD);
    expect(idCallOrder[1]).toBe(PARENT);
    expect(idCallOrder[2]).toBe(GRANDPARENT);
  });
  /**
   * The entire event registration state of the world should be "locked-in" at
   * the time the event occurs. This is to resolve many edge cases that come