Android : Android Studio: Gradle Product Flavors override project properties?

I am building different product flavors of an Android App in Gradle (Android Studio).

Hence I defined the following product flavors:

android {

    project.ext.set("customer", "")
    project.ext.set("server", "")

    //Configuration happens here - code removed for readability

    buildTypes {

        debug {
            server = "test"
        }

        release {
            server = "release"
        }
    }

    //Available product flavors
    productFlavors {
        customerA{
            customer = "a"
        }
        customerB{
            customer = "b"
        }
        customerC{
            customer = "c"
        }
    }
}

However, later on, when I access the defined project property "customer" (whose value is set in the product flavor i am currently building) it always has the value "c" even though i build customerA (in which case customer should be "a" rather than "c"). For instance I execute the following task later on:

task preBuild.doLast {
    println "Building customer: " + customer
}

and it always prints:

Building customer: c

So i am guessing there is some overwriting happening? Possibly related to the configuration VS execution phase? Not sure how/why though, so any help is be greatly appreciated.