I have a bunch of those US shares and i am now trying to get a certificate because I don't want to have a problem some day with not having one. Take my word that Zenith management is exceedingly unhappy about the existence of this gray market for their shares because they need cash and will have to do another fundraising, preferably at prices higher than the last PP and that price would be far above what these shares are currently selling at. Zenith might attempt to shut that trading down  and exclude those US shares from any possible future sale of the company but I don't know if that is possible. Anyone who does not have a certificate could be out of luck ... perhaps.