The data returned by the toArray() function does not use getter methods that may have been set up, but setFromArray() does use the setter methods. As a result, while the following code can be perfectly valid for copying a property from one row object to another:

$rowObj1->prop1 = $rowObj2->prop1

This code can fail:

$rowObj1->setFromArray($rowObj2->toArray());

Specific example - Suppose prop1 is serialized before being written to the database, and the model contains the following functions:

public function setProp1($value) {
    $this->set('prop1', serialize($value));
}

public function getProp1() {
    return unserialize($this->get('prop1'));
}

On $rowObj1, the property prop1 would be serialized twice after running $rowObj1->setFromArray($rowObj2->toArray()).

I suspect the correct solution is to have toArray() use any getter methods that may have been set up.