Odd Command Block / Teleportation behavior

Hi,

I set a command block to this command: "tp @p -179 56 -518"

What I expected to happen was...:
Get teleported to -179 56 -518

What actually happened was...:
I got teleported to 178.5 56 -517.5

It appears to be moved by one block soth and one block east

However, this can be avoided by just entering e.g. -179.3 56 -518.3

The problem is: This trick doesn't work with the arguments at playerselection. If you look at my screenshot. The commandblock should teleport anyone from the block the torch is on, to the stoneblock. (radius is 1) What actually happens is, it only detects players on the blue blocks

Am I doing somthing wrong?

Thanks in advance

waelty