[Developers] querying for values during mqlwrite?

[Augusto Callejas]

hi-

i'm able to query for mql values during mqlwrite in the queryeditor:

===
{
  "create" : "unless_exists",
  "guid" : null,
  "name" : "AlbumXXX",
  "type" : "/music/album_release_type"
}
---
{
  "create" : "created",
  "guid" : "#9202a8c04000641f80000000091ecb1b",
  "name" : "AlbumXXX",
  "type" : "/music/album_release_type"
}
===

but i can't do this using /api/service/mqlwrite directly:

===
    "messages" : [ {
      "code" : "/api/status/error",
      "message" : "Can't query for values of guid in a write, only those of
id"
    } ]
  }
===

why can i query for guid in the queryeditor, but not mqlwrite?

this is on sandbox.freebase.com if that makes a difference.

thanks,
augusto.