TextField and SearchBox in Dialog require 2 clicks to regain focus

[cnshenj]

Environment Information

• Package version(s):
  "office-ui-fabric-react": "^6.138.1",
  "react": "^16.8.1",
  "react-dom": "^16.8.1",

• Browser and OS versions: (fill this out if relevant)

Please provide a reproduction of the bug in a codepen:

https://codesandbox.io/s/91oz23zj64

1. Click the TextField in the Dialog to focus
2. Click outside the TextField (e.g. empty Dialog area) to move focus out
3. Click the TextField again

Actual behavior:

The TextField doesn't have focus, doesn't accept typing.
Click the TextField one more time, it will then regain focus.

The TextField outside the Dialog is not affected.

Expected behavior:

After step 3, the TextField should have focus

Priorities and help requested:

Are you willing to submit a PR to fix? (Yes, No)
Maybe

Requested priority: (Blocking, High, Normal, Low)
Normal

Products/sites affected: (if applicable)

[JasonGore]

This is odd in how much the behavior varies. I've also created a CodePen which also shows this issue occurring, but with varying frequency:
1. Is an issue when moving focus into CodePen IDE area and back into TextField. However even in this instance it appears to work occasionally (10% of the time)
1. Is not an issue when focus is still within "application" window or Modal.
1. Is not an issue at all in CodePen's Debug mode, even when moving focus to browser menu or outside browser.

This obviously has something to do with DOM hierarchy and may also have an async component to it.

EDIT: These observations were with an older version of Fabric and are inaccurate.

[JasonGore]

This and #8011 appear to be regressions caused by #7906.

[kenotron]

This #7906 was a fix proposed by @dzearing and addressed the issue raised. I am not sure what the right fix would be - if we revert, we would break something else...

[JasonGore]

This CodePen shows that this issue appears to have been fixed due to the merge of #8053 and release of v6.142.0. Please let me know if you see any other issues. Thanks!

[cnshenj]

This is fixed in 6.143.0