Error calling proc

I was just playing with the new proc call in 11.4.1 HF1, and had a simple example working briefly but after changing a couple of things it stopped working. I've cut my example down to the simplest I can, and it is still broken. Here is the rule:

ltm rule stg {
    partition dmz
    proc something { } {
        log local0. "in the proc"
    }

    when HTTP_REQUEST {
        [call something]
        log local0. "finished the proc"
    }
}

and this is the log output:

Jan  9 13:52:35 lb1 info tmm5[10176]: Rule /dmz/stg : in the proc
Jan  9 13:52:35 lb1 err tmm5[10176]: 01220001:3: TCL error: /dmz/stg  - invalid command name ""     while executing "[call something]"

It is too simple, it must be me, I just can't see what the problem is. Any ideas?