Child asset useful life adopting parents useful after masterdata change

Hi experts,

Let me provide an example.

Parent asset has useful life of 5 years

Child has useful life of 4 years 8 months

I go in a change a custom master data field on a custom tab, not touching anything on the depreciation tab, and save.

I go look at the asset after the above master data change, childs useful life is now 5 years.

Seems to happen only when we change a custom field.

Any ideas?

Thank you!