On the same system with other readers there is no problem.
I can finally not say exactly what it is, but in the interaction between my Transcend 32GB SD Class 10, Win 8.1 and this unit there are problems. And since it otherwise works with all other combinations, it will probably be due to the reader.
Too bad, actually I liked the device. Great connectivity and simple design. Only the short cable annoying in normal operation, but now arranged me so.