This bug can be fixed by installing the newest keyboard controller version (Zarenbourg KBC V1.18). Please refer to the corresponding point in the FAQ of this page on how to perform an update. Or download the PDF document “Zarenbourg Update”. KBC V1.18 is used for TP40 keybed. KBC V1.17 is used for the older TP100 keybed and here the black keys are louder.