MoneyField isChanged always returning true - silverstripe

Question

I have a DataObject Confirmation that looks like this:
<?php
class Confirmation extends DataObject
{
private static $db = array(
'Reimbursement' => 'Money',
'SomeText' => 'Varchar(255)'
);
private static $has_one = array(
'Page' => 'Page'
);
public function getCMSFields()
{
$fields = parent::getCMSFields();
$reimbursementField = MoneyField::create('Reimbursement');
$someTextField = TextField::create('SomeText');
$reimbursementField->setAllowedCurrencies(array('SEK'));
$fields->addFieldsToTab(
'Root.Main',
array(
$reimbursementField,
$someTextField
)
);
return $fields;
}
public function onBeforeWrite()
{
parent::onBeforeWrite();
if($this->isChanged('Reimbursement')) SS_Log::log( print_r ( 'changed', true ), SS_Log::WARN );
}
}
if($this->isChanged('Reimbursement')) in the onBeforeWrite() function will always evaluate to true. Regardless of what is being changed. Even when saving without making any changes - it will fire the log function.
Edit: Checking the stacktrace with SS_Backtrace::backtrace() in Money.php's setValue() function I find that every time I save the Confirmation DataObject, setValue() is called without passing the $markChanged parameter set to false, from DataObject.php line 1281, resulting in the $isChanged flag being set to true, and the field always behaving as if it has changed.
When logging DataObject's getChangedFields() function I get the output below (when saving without making any changes). Notice the Reimbursement field being present, and before being empty. What am I missing here?
[22-Mar-2016 16:28:07] Warning at framework/model/DataObject.php line 2597: Array
(
[Reimbursement] => Array
(
[before] =>
[after] => Money Object
(
[currency:protected] => SEK
[amount:protected] => 25000
[isChanged:protected] => 1
[locale:protected] =>
[currencyLib:protected] => Zend_Currency Object
(
[_options:protected] => Array
(
[position] => 8
[script] =>
[format] =>
[display] => 2
[precision] => 2
[name] => svensk krona
[currency] => SEK
[symbol] => kr
[locale] => sv_SE
[value] => 0
[service] =>
[tag] => Zend_Locale
)
)
[allowedCurrencies:protected] =>
[value:protected] =>
[tableName:protected] =>
[name:protected] => Reimbursement
[arrayValue:protected] =>
[defaultVal:protected] =>
[failover:protected] =>
[customisedObject:protected] =>
[objCache:ViewableData:private] => Array
(
)
[class] => Money
[extension_instances:protected] => Array
(
)
[beforeExtendCallbacks:protected] => Array
(
)
[afterExtendCallbacks:protected] => Array
(
)
)
[level] => 2
)
)