SD Card Reader with LPC43xx
This is speculation, so don't hold it to high standards :)

Difference between SD and SDHC is the fact that addresses are no longer byte based (32-bit number gives you the 4GB limit. Sandisk's website [1] says 2GB is the limit, but I vaguely remember 4GB cards in both variations), but 512B sector based.

As for 64GB, those are supposed to be SDXC, but as far as I can see the difference is just the filesystem change (exFAT vs. FAT32), which seems a bit silly, since the SD interface addresses blocks of raw data. I can't find a reference explaining any other difference, and would appreciate it. I've only used SD and SDHC on microcontroller, so my SDXC understanding could be wrong.

To actually answer: No, it definitely won't be the same bug fix (support for different commands and sector vs. byte addressing). I guess the upside is that a bugfix might not be needed at all.

[1] http://kb.sandisk.com/app/answers/detail/a_id/2520/~/sd%2Fsdhc%2Fsdxc-specifications-and-compatibility