This is the result of hinting. We can see that not only 'm' is affected, but also 'BDEGbd' have been clamped to the baseline/x-height/cap-height (compare to 'a'), and the diagonal cut-offs at the top of 'bdh' have been flattened (compare to the top of 'kl').
This is the result of hinting. We can see that not only 'm' is affected, but also 'BDEGbd' have been clamped to the baseline/ x-height/ cap-height (compare to 'a'), and the diagonal cut-offs at the top of 'bdh' have been flattened (compare to the top of 'kl').