Customer material Info:Issue with condition type missing billing document

Hi,

We are facing issue with the when we rae trying toncreate a billing document from delivery.The billing document gets created but a condition type which was there in sales order gets missed from billing documnet.

We observed that business has maintained an entry in VD52 for that material with a customer material info and if we remove that customer material info then the billing document picks up the condition type.

I would like to know where this kind of validation would be and why it's behaving like this and how can we fix this since business wants to maintain the entry in VD52.

Thanks

Umang