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No worries Pip, glad you found your answer - can you mark this question as answered? Thanks Keith

Can you paste what your code looks like. This sounds like to me that your canonical is dynamically gernerated by some code so it is taking the domain your page is located and using that instead of statically adding the domain. For instance with PHP some could add $_SERVER['REQUEST_URI'] in the header. This will take whatever the current domain name is being served. So if you are looking at your website on a desktop then your the URL is www.example.com then you would see that. If you are at m.example.com then that would appear as the canonical. make sense? Code updates generally take about a week to update.