Try the code generated by Facebook (see http://i.imm.io/1ilGp.png )? It was very useful for us to publish data samples (you just need to put your access token on your line). In addition, it is possible that the Article parameter will not necessarily work around this issue.
Everything seems OK to me (including the Article parameter). However, I have never used the Graph API to validate opengraph publishing (I always use curl or a browser), so maybe this is just a Graph Explorer explorer error.
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