RTS5129 card reader fails to read SDXC card using the new kernel drivers

Hi, I have a Lenovo Yoga 13 laptop with a Realtek RTS5129 card reader (0bda:0129)
It used to work fine with the RTS5139 kernel driver, but apparently that driver was removed since kernel 3.16 and replaced with MFD_RTSX_USB / MMC_REALTEK_USB. I upgraded to kernel 3.18.1 and compiled those drivers, and now I'm getting this kind of errors when I insert my SDXC card:

Jan  6 22:59:44 yoga kernel: [  812.978737] mmc0: error -22 whilst initialising SD card
Jan  6 22:59:45 yoga kernel: [  813.981192] mmc0: error -22 whilst initialising SD card
Jan  6 22:59:46 yoga kernel: [  815.053945] mmc0: new ultra high speed SDR50 SDXC card at address 1234
Jan  6 22:59:46 yoga kernel: [  815.054086] mmcblk0: mmc0:1234 SA64G 57.7 GiB
Jan  6 22:59:46 yoga kernel: [  815.056112]  mmcblk0: unknown partition table
Jan  6 22:59:47 yoga kernel: [  815.662453] mmcblk0: error -110 sending stop command, original cmd response 0x900, card status 0x900
Jan  6 22:59:48 yoga kernel: [  816.265726] mmcblk0: error -110 sending stop command, original cmd response 0x900, card status 0x900
Jan  6 22:59:48 yoga kernel: [  816.872253] mmcblk0: error -110 sending stop command, original cmd response 0x900, card status 0x80800b00
Jan  6 22:59:49 yoga kernel: [  817.475467] mmcblk0: error -110 sending stop command, original cmd response 0x900, card status 0x900
Jan  6 22:59:49 yoga kernel: [  818.079672] mmcblk0: error -110 sending stop command, original cmd response 0x900, card status 0x900
Jan  6 22:59:50 yoga kernel: [  818.681950] mmcblk0: error -110 sending stop command, original cmd response 0x900, card status 0x900
Jan  6 22:59:51 yoga kernel: [  819.286227] mmcblk0: error -110 sending stop command, original cmd response 0x900, card status 0x900
Jan  6 22:59:52 yoga kernel: [  820.494652] mmcblk0: error -110 sending status command, retrying
Jan  6 22:59:52 yoga kernel: [  820.495144] mmcblk0: error -110 sending stop command, original cmd response 0x900, card status 0xb00
Jan  6 22:59:52 yoga kernel: [  821.100047] mmcblk0: error -110 sending stop command, original cmd response 0x900, card status 0x900

(etc)

Sometimes I'm just getting the "error -22" messages.
The card is a Toshiba 64GB SDXC class 10, UHS 1. It works fine with an external USB card reader. Also, I tried another card, a Transcend 16GB SDHC class 10, and it works fine in the laptop's card reader.

Please help investigate this problem and let me know if I should do something on my side.

Thanks
Adrian