Recover the USB-Mass Storage mode in ET1-JB

The ET1 JB uses MTP and PTP to connect to a PC. We have noticed that both modes do not work properly if there are too many files on the SD card (by many, we mean hundred of thousands). In that case, files are visibles on the SD card if we use the ET1 file browser; but they are not visibles on PC. And many failures arise if we try to copy a new file from PC to the ET1. We've tried several ways: toggling the MTP/PTP modes; unmount/remount the SD card; reboot the tablet. We also tried to connect the ET1 to another PC, without success.


Is there a way to recover the USB-Mass Storage mode? Or any other solution to make MTP/PTP properly working in presence of many files?