I have noticed the same with  �cancel �.
 
In the online British English dictionary that I just checked,  �travelled � is the past tense. (Cambridge)
 
In the American one, both  �traveled � and  �travelled � are listed side by side.
 
I have been told in the past that in some cases (as language natually changes etc) that both can be used for  �canceled � and  �cancelled �.
 
I am sorry that this is not a definitive answer.
Perhaps there is not one definitive answer in this (these) case(s).