You will have to ask AC and/or LH as to the reason for this anomaly, but them's the rules...
"Mileage accumulation on Lufthansa is 100% of actual miles flown on North-Atlantic flights in all classes. Accumulation on non-North-Atlantic flights in economy class is 50% of actual miles flown (minimum 500 miles)."
https://www.aeroplan.com/en/collect/air_lufthansa.jsp
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The Star Alliance Award Comparison Chart