As Aldiko still just closes all support requests without answering, I contacted Google for a refund. And I got the refund.
So, as a result people should clearly thing before buying Aldiko with regard to the support policy and the behaviour in fixing bugs.
HTC One (M8) (KOT49H, O2_206, InsertCoin M8 2.6.0 | 1.54.401.5 | Android 4.4.2 Sense 6)
Samsung Galaxy Note 10.1 2014 (rooted, JB 4.3, XUAMJ9)