You should use FAT16 filesystem instead of FAT32. You can also use either a partition or the whole device, it doesn't matter. I had the same issue, and in my case I formated my mp3player with the following command:
root:~# mkdosfs -n IAUDIO -F16 -f2 -v /dev/sdb1 mkdosfs 3.0.16 (01 Mar 2013) /dev/sdb1 has 65 heads and 62 sectors per track, logical sector size is 2048, using 0xf8 media descriptor, with 1024640 sectors; file system has 2 16-bit FATs and 16 sectors per cluster. FAT size is 64 sectors, and provides 64030 clusters. There are 16 reserved sectors. Root directory contains 1024 slots and uses 16 sectors. Volume ID is 1034e7d3, volume label IAUDIO .
And now it works as it should.