This is just silly - David Douglas Duncan, who is one of the few photographers that Leitz ever gave a custom serial number to (serial number M3D), was famous for using non-Leitz glass. From his book <i>Great Treasures of the Kremlin</i> "All of the photographs were taken on Kodachrome with two Leica M3D cameras fitted with Canon, Nikkor and Zeiss-Biogon lenses."
Enjoy your Canon lense. The link to history is one of the enjoyable things about using mechanical cameras like the M4-2.
Shooting with: Leica CL, Canonet QL 17 GIII