dropped source won't redrag from one target
I've got a fairly simple drag and drop interaction, but the drop source gets stuck on one target.
I'm using Captivate 2017 and working in html5 with non-responsive project.
I have only one source and four targets--one correct and three incorrect. The interaction is set to autosubmit correct answer and redrag dropped sources. I can redrag the source when it is dropped on two of the incorrect targets, but it will not redrag when dropped on the third target. I have a shared action that each incorrect target triggers. I made sure the targets are above all the other items in the timeline and the source is above all the targets.
I can't find anything different between the targets that will allow redragging and the one that will not. What settings could possibly cause this?
Here's a screenshot of the relevant part in captivate and then stuck in html5 preview.

