At first, sorry for my bad english

I think I found a bug in ptif creation.
The command "convert -debug Exception image.jpg -define tiff:tile-geometry=256x256 'ptif:image.tif'" fails with the next exception :
2011-11-01T13:22:39+01:00 0:09.340 15.840u 6.6.0 Exception convert[5591]: tiff.c/TIFFErrors/493/Exception
4608: Col out of range, max 4607. `image.tif'
2011-11-01T13:22:40+01:00 0:09.630 16.290u 6.6.0 Exception convert[5591]: tiff.c/TIFFErrors/493/Exception
2304: Col out of range, max 2303. `image.tif'
When I run the same command with a tile size of 272x272, it works perfectly.
My image has a size of 4608x3456. It turns out that 4608 / 256 returns an integer, which a think is the problem.
My version of IM is 6.6.0-4, the default package of ubuntu.
Thanks.