Projection

I do not know if this is a bug. A 51st level conjurer cast's 'projection', he leaves his body and floats around in astral projection. Then anyone can slay his physical body as it lays in a state of coma. Even a level 11 thief? I found that out the hard way. Then I tested it to be sure even a very young person could kill the comatose body. The young person could. Just wondering if this is by design. Not a problem for me if it is. Very cool spell. Thank you