[Bug] Group Shifting Out of Artboard
### Bug report
#### Expected behavior:
I name a 375pt wide background layer **bg [16 16 16 16; width>=375]**, then place a text layer over the background layer. I move the text layer 16pt from the left edge of my 375pt wide artboard. I expect the text layer and background layer to stay where they are.


#### Actual behavior:
What happens instead is, the layer group shifts -135pts to the left, off of the artboard. When putting the background layer back to x:0, the text layer shifts into the center of the group.



#### Steps to reproduce:

1. Create a group
2. Add a background layer shape to the group
3. Add a text layer over the background layer in the group
4. Position the background layer to X:0, Y:24
5. Position the text layer to be centered in the background layer, and X: 0
6. Rename the background layer **bg [16 16 16 16; width>=375]**
7. The group shifts, the rearranging the layers results in an endless loop of moving stuff


#### GIF Demonstration
![paddybug-shiftingleft](https://user-images.githubusercontent.com/873222/38201794-772cd306-3667-11e8-9082-0166009f0f72.gif)

