With this code:

void take(owned uint8[] ar, size_t filled) {
    stdout.printf("take ar.length=%lu filled=%lu\n", ar.length, filled);
}

void main() {
    uint8[]? ar = new uint8[1024];
    take((owned) ar, ar.length);
}

With Vala 0.22.1, this is printed:

take ar.length=1024 filled=1024

With Vala 0.23.1 (and master 9035483cb as of typing this), this is printed:

take ar.length=1024 filled=0

Looking at the 0.23.1 generated C code, ar_length1 is being set to zero (ownership is being transferred) before the parameter is passed to the method.