I’ve noticed that map reports resulting from a Drag and Drop move of a piece get output to chat even when the Drag and Drop triggers a set of commands that make the report invalid (e.g. a command intended to prevent a piece being moved incorrectly).
My guess is that this is working-as-designed and the “Drop” is not seen by Vassal as part of the overall command ? And yet, a single UnDo does UnDo the whole thing, including an “UnDo” of the report to chat.
Workaround might require dispensing with in-built map reporting.