why does mkfs.xfs complain here?

[Michael Monnerie]

# mkfs.xfs -f -L ws1phptmp -b size=4096 -d su=65536,sw=4,agcount=4 -i attr=2 -l lazy-count=1,su=65536 /dev/sdf1
log stripe unit specified, using v2 logs
Allocation group size (65262) is not a multiple of the stripe unit (16)

Why is above error generated at all? Shouldn't mkfs.xfs handle that 
situation and change agsize automatically? If I then do:

# mkfs.xfs -f -L ws1phptmp -b size=4096 -d su=64k,sw=4,agsize=65262b -i attr=2 -l lazy-count=1,su=65536 /dev/sdf1
log stripe unit specified, using v2 logs
agsize rounded to 65264, swidth = 64
meta-data=/dev/sdf1              isize=256    agcount=4, agsize=65264 blks
         =                       sectsz=512   attr=2
data     =                       bsize=4096   blocks=261048, imaxpct=25
         =                       sunit=16     swidth=64 blks, unwritten=1
naming   =version 2              bsize=4096
log      =internal log           bsize=4096   blocks=1200, version=2
         =                       sectsz=512   sunit=16 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

So no problem using agsize instead agcount, where agcount complained
about group size = 65262, which I then used without problem?

mfg zmi
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