In the (non-canon) LEGO Star Wars New Yoda Chronicles, Qui-gon appears as a Force ghost in response to a call for help from Obi-wan's ghost and Yoda. It was a mistake, as Yoda and Obi-wan were communicating through the Force to someone else.
Not wanting to offend Qui-gon, Yoda lies and tells him they needed help opening a pickle jar.