I was attempting to use earthen with organic groups, however I noticed that (attached) issue when viewing content posted to a group. I created two pieces of content with the same text, one posted to a group and one not posted to a group. The content posted to a group overruns into the right sidebar.
I was trying to inspect the elements and here's what I've noticed... but I'm not really a css expert so figure out how to fix it.
For non-group posts the trail goes:
... contentLayout -> content -> Post -> Post-body -> Post-inner -> PostContent -> Post -> Post-body -> Post-inner -> PostContent -> article
For group posts the trail goes:
... contentLayout -> content -> Post -> Post-body -> Post-inner -> PostContent -> node-5 -> content
So quite a bit is cut out for group posts, especially the article class.