At the moment, you need to hold the mouse click and leave the mouse over the item until it flashes then it can be dragged.
There's a flaw with my input helper lua module. Once the hold test is activated, it still updates the position. This means if the mouse position has left the test zone by the hold time is triggered, the drag initiation test fails.
This was legacy code to handle drags before I realised needed to have a different approach to handle a touch interface.
This issue was a bit of code blindness for me. I know exactly how everything works, so my muscle memory automatically compensates for the quirk.