I have here a 64GB Micro SDHC card. It is not labelled as SDXC, its manufacturer has quite clearly labelled it as SDHC. While this is not my supplier, the image at http://www.militarygrade.org/blog/2014/06/military-certified-compact-por... appears to be of the same card.
I have a large number of music files on my hard drive, and am trying to transfer them onto a 32 gigabyte (31.2 usable) micro SDHC card so I can listen to them using my cellular phone; the transfer always fails.
I'm running Windows 8 - Core X86-64, and my laptop has an SDHC card reader so I'm using a SDHC to micro SDHC adapter.
I have a 4GB Kingston class 4 4GB micro SDHC card that I use for backing up files using my personal rsync script. On 10.04, 10.10, 11.04 it worked fine on the 32 bit OS. On 64 bit 11.10, files fail to be copied; sometimes they appeared to be copied, ls does not find the files but df -kh shows that disk space has been taken up.