New item does not appear in TransitionMotion when used in staggered mode

Passing a function to TransitionMotion.props.styles works on initial load but does not update when additional items are added to the array.

Start by reproducing the issue with TransitionMotion in staggered mode, passing a function to props.styles and then adding an item to the array. Trace the TransitionMotion entry point and verify that newly added items receive updated styles; done means the new item animates and appears without regressing the initial-load behavior.

Written by the indexing model from the issue text.