MapStruct cannot find class generated by @KotlinBuilder when using @AfterMapping

Using:
api 'org.mapstruct:mapstruct:1.3.1.Final'
kapt 'org.mapstruct:mapstruct-processor:1.3.1.Final'
api "com.github.pozo:mapstruct-kotlin:1.3.1.1"
kapt "com.github.pozo:mapstruct-kotlin-processor:1.3.1.1"

Issue:
The target Product is a kotlin data class with @KotlinBuilder.
This works: fun mapToModel(source: ProductDto): Product
But when adding this

    @AfterMapping
    fun afterMapToProduct(source: ProductDto, @MappingTarget builder: ProductBuilder) {
       // fun stuff
    }

Then the ModelMapperImpl class contains the package import: import error.NonExistentClass;

When I don't have this @AfterMapping the impl class correctly contains
import dk.bnr.androidbooking.model.product.ProductBuilder;
and correct building method.

I suspect its a mapstruct issue, but I'll cross-post issue 7 in KotlinBuilder with link to here, in case I'm wrong

Reproduce the issue using the MapStruct and KotlinBuilder dependencies listed in the report, with the Product data class, ProductDto, @KotlinBuilder, and @AfterMapping method. Compare the generated ModelMapperImpl output with and without @AfterMapping, focusing on the ProductBuilder import. Done means the generated implementation resolves the builder class instead of importing error.NonExistentClass.