Reproduceable panic on -CURRENT

Hello,

I'm running -CURRENT from yesterday and i'm experiencing a fully reproduceable
panic while trying to mount a usb mass storage device.
Filesystem is fat32. 

portatile# mount /mnt/da0s1/
mount_msdosfs: /dev/da0s1: Permission denied
g_vfs_done():da0s1[WRITE(offset=17408, length=4096)]error = 13
fsync: giving up on dirty
0x3c301d330: tag devfs, type VCHR
	usecount 1, writecount 0, refcount 128 mountedhere 0xc2f35900
	flags()
	v_object 0xc304aa50 ref 0 pages 125

		dev da0s1
panic: wrong offset 17408 for sectorsize 3263072112
KDB: enter: panic
[thread pid 48, tid 100049 ]
Stopped at	kdb_enter_+0x30: leave
db> where
Tracing pid 48 tid 100049 td 0xc26c5960
kdb_enter(c08dbdb2,c09a3a80,c08d694f,e53c5b90,100) at kdb_enter+0x30
panic(c08d694f,4400,0,c27e8770,c3057840) at panic+0xce
g_io_request(c3057840,c27e8740,a00000a4,d67637d8,e53c5c0c) at g_io_request+0xbf
g_vfs_strategy(c301d3f0,d67637d8,c08da0d1,235,d67637d8) at g_vfs_strategy+0x56
bufwrite(d67637d8,d67637d8,e53c5c4c,c06ca369,d67637d8) at bufwrite+0x168
bawrite(d67637d8,0,c08e3ff2,198,c301d3ac) at bawrite+0x65
vop_stdfsync(e53c5ca4,0,e53c5ca4,e53c5c78,c08860ce) at vop_stdfsync+0x148
devfs_fsync(e53c5ca4,c301d330,c301d3f0,c301d330,e53c5cc0) at devfs_fsync+0x2f
VOP_FSYNC_APV(c0936ac0,e53c5ca4,c26c5960,5d1,c2a76400) at VOP_FSYNC_APV+0x9d
sync_vnode(c301d3f0,c26c5960,c08e48ef,608,0) at sync_vnode+0x154
sched_sync(0,e53c5d38,c08d94e5,30d,0) at sched_sync+0x236
fork_exit(c06d2b4f,0,e53c5d38) at fork_exit+0xc2
fork_trampoline() at fork_trampoline+0x8
--- trap 0x1, eip = 0, esp = 0xe53c5d6c, ebp = 0 ---
db> show alllocks
Process 48 (syncer) thread 0xc26c5960 (100049)
exclusive sleep mutex Giant r = 0 (0xc09a37e0) locked _at_ /usr/src/sys/kern/vfs_subr.c:1533

Thanks for your attention and help
Filippo