flag error

I only saw this film once and barely caught a big error. There's a group squatting around a map discussing the dispositions of various allied forces. Mention is made of the First Canadian Army to the North and on the map you can just make out a Canadian flag at the top of the paper. The problem is that the flag shown is the modern Canadian flag which was only adopted in February 1965! Before that, it would have been the Red Ensign.