[TYPO3-mvc] ObjectStorage not initialized at frontend request

[Zalán Somogyváry]

Hi list,

I've found some strange behaviour of extbase, when creating a model object in the frontend.
Within an action an object is retrieved from a repository, the object is retrieved, but the associated objectStorage seems not to be initialized by the repo:
I always get this error:
Fatal error: Call to a member function attach() on a non-object in /Path-to-myobject/MyObject.php on line #.
but the constructor of my object has:
$this->variable = new Tx_Extbase_Persistence_ObjectStorage();

Any suggestions? I've already debugged and debugged but can't find a reason for this...

Best regards,
Zalán Somogyváry