If you tell the command block to place a block at 223 64 -289, it places the block at 223 64 -287. Not nine, but seven! Two more then I want.
Environment
OS is OS X 10.8.4, Processor is 3.2 GHz Quad-Core Intel Xeon, Memory is 6GB 1066 MHz DDR3, and Startup Disk is Macintosh HD. (This is the "About this Mac" window info. I don't THINK this matters, but hey, you never know.)
I can confirm it only happens in the negative directions. Placing a block at 0,Y,0 and trying again at -1,Y,-1 will atempt to place the block at the exact same location.