I have a similar issue since trying out a "new" CMR in the development area.
SD doesn't mount in Recovery or in ROM, it is detected during fastboot.
Starting the phone with the SD card inside makes it bootloop.
The SD card is visible on linux and windows. I've formatted it to FAT in any case but it makes no difference.
ADB & "USB debugging" is not activated when a cable is plugged in when in ROM. Drivers and settings are fine.
All I could do is fastboot and apply RUU.... but even this didn't solve the issue...
Is it possible to repairable "brick" USB and SD card mounting with an issue in Recovery?
Please help, I cannot really use the phone without SD card, FW 1.5 is not my favourite...