Command block tp argument problem

whenever you try to use a command block with a player or @a[x,y,z] that is intended to be teleported it fails to complete the task and says in the 'previous output' box,"You must specify which player you wish to perform this action on." From what I've experimented with this is the only instance where this happens, but it most likely applies to other commands(actions).
For example:

tp @a[637,231,189]328,161,244

will fail to work and will display the 'specify player' text.
I hope you are able to fix this issue in the next snapshot as it is a nuisance. to redstoners.
Thanks for your time.