Dynamic Batching breaking by transform.position?

I am experiencing a curious problem.

I have a bunch of simple quad objects (2DToolkit sprites) using the same atlas. When I run the game, batching seems to work and my drawcalls stay at around 30-40 as I display more of these objects. I actually have an object pool of 300, which are instanced at the beginning, so I am just activating them so they display.

Now, if I add this line to my objects' update loop:

 myTransform.position = newPosition;

the batching breaks and my draw calls linearly grow as I activate more objects from my pool. (the draw calls grow steadily from 40 to around 250+).

Commenting the line will make batching work again. But of course I need my objects to move around :) so I need to change their position.

Any ideas on how to correct this problem?