Construction type is automatically set from &2 to &1

What causes this issue?

Synchronous maintenance of material number and construction type is
intended for this type of equipment in Customizing, or to be more
precise: If the material number is maintained, then the construction
type must have the same value.

System Response

The assembly type of the equipment previously had the value &V2&. The
system automatically changes the material number value to &V1&. durch.

How to fix this error?

Changes to synchronously maintained values can only be made using the
material number. If you do not want this synchronous data storage, you
should either change the type of equipment or change the Customizing
settings.

Error message extract from SAP system. Copyright SAP SE.