The problem was a beginner's mistake I made to add another widget:
document.body.innerHTML = document.body.innerHTML + ...;
That apparently reset gsap's event handling code. Adding the proper way, document.createElement(...) with document.body.append(...) made the problem disappear.
I still don't understand why the DOM DnD event handlers were added in particular situations instead of emptyFunc() (which I think cannot be seen by logging since the DOM lacks the necessary tooling) but my immediate problem is resolved. @OSUblake and @Cassie, I appreciate your help.
