The McIntosh MA252 does not use an old-style rheostat for volume control. Instead, its electronic attenuation system (reflected in the volume display) follows a logarithmic attenuation curve. As a result, the volume increase per step is not uniform; in some regions, each step may represent a larger change than in others.
It is quite possible that the 52–53 transition crosses one of these regions where the attenuation curve changes slope. My Cambridge Audio Azur 851A integrated amplifier has a similar type of volume control behavior, and I can also notice a slight jump at certain points on the dial.
On my system, the jump is noticeable but still within expectations. If you feel the step change is unusually large compared to normal behavior, it may be worth raising the question with McIntosh for confirmation.