Second Curtain Flash wireless Canon v Yongnuo

Can anyone enlighten me as to why on earth canon speedlites and transmitters wont work in second curtain flash mode wireless , however the Yongnuo copy transmitter and flashes do and in fact the yongnuo transmitter sends the info to a canon flash and works fine but using the canon transmitter wont work , cant work out any sense in this ? , my YN transmitter is however poorly made and falling to bits so having to botch it to get it working and would have rather relied on the Canon !!....

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Wedding Photographer North East & North Yorkshire, Northumberland & Wedding Photographer Cumbria