[TYPO3-mvc] Parent class properties not available

[Bernhard Schenkenfelder]

Please consider a simple model consisting of two classes:

Trip
* title
* image

and

Cruise (extends Trip)
* dates

In theory, a $cruise object contains the above three properties, all of which are accessible through their respective getters and setters. However, from time to time both getTitle() and getImage() return null, whereas getDates() always returns the correct value. Flushing the cache resolves the problem temporarily, not permanently.

Any ideas where this is coming from?