Is it normal for mother to compensate son for gifts to daughter's children

I am the mother of 3 children. My mother gives presents (b-day/christmas, etc.) to her grandkids on every occassion. I found out that my brother (the uncle of my children) who has no children, expects our mother to compensate him, dollar for dollar, on money she spends on my children, her grandkids. Moreover, my mother does it. In other words, if my mother spends $50.00 on a gift to one of my kids, she has to pay my brother $50.00 cash I say this is abnormal. What do you think?