Test Case:

https://fiddle.sencha.com/#view/editor&fiddle/2lp9

1) Click the button on in the fiddle.
2) Observe that when the dialog shows, the "Name" label is above the field, then it repositions itself inside the field where it should be.

The flicker needs to be eliminated. Also note that this appears to have been introduced between 6.5.0 and 6.5.1.

The issue occurs because of animation, because it doesn't execute the code to position the label until the animation completes.