In message , at 23:11:55 on Sat, 1 Mar
2014, tim..... remarked:
click on the "link" button, check the "Short URL" box within the popup
dialogue

Are you logged in? That seems to be a recent innovation/requirement.

though I can't confirm that they last long enough to post to someone else

As far as I know the short links last a long time.
--
Roland Perry