[solved]
 

Same problem. Here is how I solved it, and details below for symptoms as I was encountering the same problem.

SOLUTION:

I inserted the thumb drive and waited 5 seconds for it to auto mount.
Then I use a console window to manually issue the umount command:
Once I did that it was not mounted, but it was still recognized as a 8GB drive. You can tell in Disk Utility. At that point I was able to install System Rescue CD from ISO onto the USB drive.

PROBLEM:

I have a brand new Transcend Micro 8GB thumb drive that I want to use to put a SystemRescue ISO onto.

I can insert the thumb drive and it shows up in Nautilus. There are a few files on the device and it's reported as an 8GB drive. But if I try to unmount it then it's reported as a drive with zero MB and I can't format it

Disk Utility sees it, but won't let me format it because it's "busy" when it's mounted, and it's "empty" when it's unmounted.

sudo fdisk -l

Disk /dev/sdf: 8103 MB, 8103395328 bytes
196 heads, 32 sectors/track, 2523 cylinders
Units = cylinders of 6272 * 512 = 3211264 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xc3072e18

Device Boot Start End Blocks Id System
/dev/sdf1 * 1 2524 7913456 c W95 FAT32 (LBA)

sudo tail -c 0 -f /var/log/syslog

Jan 30 22:08:50 greg-laptop kernel: [692463.768973] usb 2-1: new high speed USB device using ehci_hcd and address 9
Jan 30 22:08:50 greg-laptop kernel: [692463.903429] usb 2-1: configuration #1 chosen from 1 choice
Jan 30 22:08:50 greg-laptop kernel: [692463.903878] scsi15 : SCSI emulation for USB Mass Storage devices
Jan 30 22:08:50 greg-laptop kernel: [692463.904256] usb-storage: device found at 9
Jan 30 22:08:50 greg-laptop kernel: [692463.904261] usb-storage: waiting for device to settle before scanning
Jan 30 22:08:55 greg-laptop kernel: [692468.905004] usb-storage: device scan complete
Jan 30 22:08:55 greg-laptop kernel: [692469.260589] scsi 15:0:0:0: Direct-Access JetFlash Transcend 8GB 1100 PQ: 0 ANSI: 4
Jan 30 22:08:55 greg-laptop kernel: [692469.261903] sd 15:0:0:0: Attached scsi generic sg5 type 0
Jan 30 22:08:55 greg-laptop kernel: [692469.262733] sd 15:0:0:0: [sdf] 15826944 512-byte logical blocks: (8.10 GB/7.54 GiB)
Jan 30 22:08:55 greg-laptop kernel: [692469.275074] sd 15:0:0:0: [sdf] Write Protect is off
Jan 30 22:08:55 greg-laptop kernel: [692469.275083] sd 15:0:0:0: [sdf] Mode Sense: 43 00 00 00
Jan 30 22:08:55 greg-laptop kernel: [692469.275089] sd 15:0:0:0: [sdf] Assuming drive cache: write through
Jan 30 22:08:55 greg-laptop kernel: [692469.278330] sd 15:0:0:0: [sdf] Assuming drive cache: write through
Jan 30 22:08:55 greg-laptop kernel: [692469.278333] sdf: sdf1
Jan 30 22:08:55 greg-laptop kernel: [692469.282200] sd 15:0:0:0: [sdf] Assuming drive cache: write through
Jan 30 22:08:55 greg-laptop kernel: [692469.282203] sd 15:0:0:0: [sdf] Attached SCSI removable disk