As soon as I read the article on WordPress about being able to share to Tumblr, I set it up and wrote a post. Everything went OK because the text preceded the photo and it was the text that showed up in the extract on Tumblr.
Everything did not go well with the second post because the image came first and, as with most of my images, I had captioned it.
The coding that sends the extract winging off to Tumblr did not like the captioning code and it messed it up.
I reported it to Support at WordPress and they acknowledged the problem and emailed me to confirm when they cured the issue.
So this is a short post to test this out.
This is the link to the Tumblr site and you can see whether the ‘share’ worked OK.
Update
Oh, oh…
It copied OK but the shape is all squished.
Photograph Works 
I’ve just set up a Tumblr account. I have yet to figure out the advantages of having one. I’ll try and post a picture to it shortly … Could it have something to do with the theme in Tumblr … that the picture got distorted?
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It’s entirely possible that it is the Tumblr theme that is causing the ‘squashing’ problem. I mentioned this when I first contacted Support (that it might not be WordPress that was causing the frames/captions issue. But, of course, it turns out that it was WP that had the problem and it may be that it is WP that is causing the squishing problem.
Advantages of Tumblr. Take a look around some sites – there are some very positive, responsible, creative people there – (and yes, plenty of cute cats as well) I guess what I am saying is that I have developed an attitude to different platforms – WordPress.com is generally polite and towards the middle of the road. Tumblr is more edgy – definitely worth exploring.
What is your tumblr URL ?
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http://mewpurr.tumblr.com
Yes! I’ve seen awesome stuff in Tumblr, but I meant … the practical advantages, like … there are no comments and stuff like that?! I realize it’s handy to post there from your phone but… more?
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People repost and ‘favourite’ things they like.
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I posted. Why, oh why, did just a little excerpt show up in Tumblr? Now I don’t know if it’s WP or me?
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It’s designed to show just an excerpt as far as I can see. And then link back to your WP post.
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but how did you get the picture in then?
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You have to put an image first, above any text, in your WP article.
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Ahhhah! Thanks! 😀
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Hi, I work at Automattic/WordPress.com. Thanks for helping us make Publicize:Tumblr better!
We’re pretty sure we’ve fixed this problem. If you find more issues, please contact our Support team.
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The fix for image-squishing works – just tested it. with https://photographworks.wordpress.com/2012/06/07/sharing-to-tumblr-resolved-second-attempt-with-pelican/
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