Wp-calypso: Sharing: Twitter sharing button does not tweet username

[ajaykj]

Steps to reproduce

1. Go to https://wordpress.com/sharing/buttons/ and enable Twitter sharing button
2. Add your Twitter @ username on the same page in the Twitter username box. Save changes. (This will be included in tweets when people share using the Twitter button.)
3. Go to https://wordpress.com/sharing/ page and connect "Twitter" to your Twitter a/c (This step is necessary for sharing button option to include the TwitterUsername in the tweets.)
4. Go to a single blog post on the site; scroll to the sharing button section; Click Twitter button

What I expected

The Tweet to have via @ MyTwitterUsername.

What happened instead

The Tweet contains via @ wordpressdotcom

Screenshot / Video

Context / Source

499791-hc, 1206962-zen

[twhite96]

I'd like to jump on this. I can take some time this weekend to patch it. That alright?

[KokkieH]

We're getting a lot of reports about this via Twitter.

[sarahcada]

Also reported here: 1207964-zen

[cafenoirdesign]

I'm seeing this issue for clients on VIP (#78910-z)

They set their sharing prefs using the Settings page _wp-admin/options-general.php?page=sharing_
They aren't using Calypso, but this issue is still occurring.

[sophiegyo]

Also reported here: 1207767-zen

[iamgabrielma]

Reported here: 1207636-zen

[roccotripaldi]

Working on a fix now!

[roccotripaldi]

this should be fixed in r-176596