Drag and Drop list ordering issue

#### What is the expected behavior?
I am trying to reproduce the simple drag and drop list ordering example from here: https://material.angular.io/cdk/drag-drop/overview

#### What is the current behavior?
However, the dragged item always snaps back to its original place. The ordering animation is showing. The event shows that the previous and the current index are always 0.
https://i.imgur.com/1RkV6MT.gifv
https://i.imgur.com/k4wMbt3.gifv

#### What are the steps to reproduce?
The drop listener and the test data:
```
strings = ["dsfs","fgjdf","ghama","jéép"];
drop(event: CdkDragDrop) {
console.log(event);
moveItemInArray(this.strings, event.previousIndex, event.currentIndex);
}
```
The HTML:
```

```
The CSS is copy-paste from the tutorial
#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Angular: 6.2.1
Material: 7.2.1
OS: Ubuntu 16.04
TypeScript: 3.2.2
Chrome: 65.0.3325.146

Start with the reproduction in the issue and compare its markup with the Angular Material CDK drag-and-drop overview. Inspect the cdkDropList and cdkDrag setup, then verify the drop event's previousIndex and currentIndex while dragging between items. Done means the dragged item remains in its new position and the list data is reordered.

Written by the indexing model from the issue text.