Yes, this is not unusual.
Even though this is contributory ESA, payments will still be reduced by 50p for every £1 of pension over the £85 per week disregard.
It is important to notify DWP about the pension, even if it is below the £85 per week, in order to prevent problems if/when it comes to their attention in the future.
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
