When you share a post with a link (and photo), you might have noticed this:
There are shortlinks in Facebook and Twitter, but no links in Pinterest and Tumblr.
This is not a bug. This is because the way Pinterest and Tumblr handle links is different from Facebook and Twitter.
When you post a link (with photo) to Pinterest / Tumblr, the link automatically gets attached to the post. So, when someone clicks on your Pinterest pin or Tumblr post, they are automatically taken to the link.
In Facebook and Twitter, when you post something (and share it as a photo, by checking the box “Share as an image post”), there won’t be any link when it is posted. When someone clicks on this Facebook post or Twitter tweet, it will be just a photo with no link to go to.
This is why we add the link by default for Facebook and Twitter. For Pinterest and Tumblr, the link is not required as it will get attached to the photo you are posting, automatically.
You can, however, add any text (and link) in the Pinterest and Tumblr boxes too if you want to.