geli bugreport? fdisk error with non default sector size

[OxY]

hi!

i tried to encrypt my root partition and the whole hard disk..
used this cmd to initalize geli:
#geli init -b -s 4096 -l 256 /dev/ad2

it succed, but after then i tried to use 
#fdisk -f part.cfg /dev/ad2.eli 

and it gave me an error: length must be multiple of sector size..
when i gave 4096,8192, so on to length the error was the same..
i tried to init the provdier without -s switch, then the fdisk ran without
any error..

did i do something wrong or is this a bug?
thanks!