When you paste a link into Known, if it’s something like a youtube video (or Soundcloud or Gist if you use my plugins), it’ll attempt to expand the link into a displayable embed code.
Trouble is, when you used a link shortening plugin, this url was changed and the display got broken.
I have submitted a patch upstream which modifies the link display code with a hook which a link shortening tool can listen to, and expand links where appropriate.
When you apply this patch, the latest version of the bitly link shortening plugin will be able to expand links within a post, caching them against the object for future reference.