PHPStan inheritance & property types

I have trouble passing PHPStan tests because of parent/child classes (besides, code runs well). These two kind of errors always show up:

• Parameter #1 $a of method xxx expects ConcreteChildClass, AbstractParentClass given
• Property ClassName::$a (ConcreteChildClass) does not accept AbstractParentClass

Here is the code (must be compatible with PHP 5.6):

<?php

abstract class AbstractClassA
{
    /**
     * @return static
     */
    abstract public function postProcess();
}

class ConcreteClassA extends AbstractClassA
{
    /**
     * @return ConcreteClassA
     */
    public function postProcess()
    {
        return $this;
    }
}

abstract class AbstractClassB
{
    /**
     * @return AbstractClassA
     */
    abstract public function deserialize();

    /**
     * @return AbstractClassA
     */
    public function someMethodA($params)
    {
        return $this->someMethodB();
    }

    /**
     * @return AbstractClassA
     */
    public function someMethodB()
    {
        $object = $this->deserialize();

        return $object->postProcess();
    }
}

class ConcreteClassB extends AbstractClassB
{
    /**
     * @return ConcreteClassA
     */
    public function deserialize()
    {
        $object = new ConcreteClassA();
        // some assignements

        return $object;
    }
}

And how this code is used:

class SomeClass
{
    /** @var ConcreteClassA $propertyA */
    public $propertyA;

    /** @var ConcreteClassB $propertyB */
    public $propertyB;

    public function someMethod()
    {
        $this->propertyA = $this->propertyB->someMethodA($params);
        $this->someProperty->someOtherMethod($this->propertyA);
        // again, someOtherMethod expects ConcreteClassA but AbstractClassA given...
    }

I tried to "play" with @template without success...

Please also note that I have limited control over abstract classes.

Thanks,