Testfor bugs

Put the summary of the bug you're having here

What I expected to happen was...:
What i expected to happen was when i put in my command:
"testfor @p[x=-160,y=4,z=-308,r=2]" or "testfor @p[x=-160,y=4,z=-308,dx=-161,dy=4,dz=-308]" the command would follow through.
What actually happened was...:
What actually happened was this error message: The entity UUID provided is in an invalid format, with no explanation on what's wrong. However if i changed the command to just "testfor @p[x=-160,y=4,z=-308]", the command followed through properly.

Steps to Reproduce:
1. Put the command in the what i expected to happen section into a command block;
2. Activate the command block;
3. error message appears