Why are the textbox not editable and shows the lock icon in packing slip journal of dynamics ax 2012?

The issue that I've been trying to solve is that sometimes the text boxes are grayed out and it shows the lock icon, when supposedly these text boxes are not grayed out and it shows some information about the shipment tracking.

This issue is intermittent. see screencast: screencast.com/t/pJED9DDekcf9

What could be the cause of this issue and how do we solve it?

Thanks!