I was struggling with the same issue (WordPress Multisite with MSLS for various languages) and made one discovery. I haven't tested this extensively so I'm not quite sure if this is "reproducable" or if it can help others but...
It seems to me that part of the problem resulted from the permalink structure of your WordPress. Furthermore whenever more than one category was selected for a particular post LinkedIn would have difficulty interpreting the link.
The solution I found to work was to de-activate all categories but one (Additional note: for some reason it seems that it's best to not choose "news" as the active category) and click update. Then try and copy-paste the link in the LinkedIn update field.
If the link is interpreted ("swallowed") correctly by LinkedIn, you can post the update and if this is important choose to re-activate other categories on your WordPress post.