Group lights screw up

hey, for a scene i’m making a scene for a new project of mine, and because i’m using a large selection of regular street-lamps i’ve been making groups and adding the groups of streetlamp model, and lamps to the scene.

the row of street lamps look like this in the non-render window:

but then when i render, the lamps get moved along for no obvious reason:
(sorry that the image is so dark)

the model and lamps are all in the same group, and their on a different layer
the lamp objects are repeated using an array modifier, but the lamps are individually placed and added to the group

any ideas what’s going wrong?

i can post the .blend if that’ll help
thanks in advance