DataCaster not working

Hi guys, 

I might have a pretty similar problem, hence I decided to hijack this thread. 
Disclaimer right upfront: I am talking about proprietary company code, so I need to pay attention to not leak to much information. 
I will still try to provide as much info as possible. 

Let's say I have Cart Entity and I have a Quote Entity, and I want to iterate all of the Quotes inside a Cart to see which one is active. 
So I foreach through the Quotes in the Cart, and on every one of them call

PHP Code:

$quote->__get('is_current') 


. 
The call to __get calls into the system/Entity/Entity magic method, which then calls

PHP Code:

$this->castAs(...) 


, which in turn tries to access

PHP Code:

$this->dataCaster 


.
This is where the rock hits the bird and the application dies due to $this->dataCaster being uninitialized - what I cannot understand given that this should have been initialized in the constructor of Entity. 

Any clue what I might be doing wrong?