Python node: transaction weird behavior

Hi folks, I’m not sure if this is an issue with Python, Revit API or Dynamo, but I have this:

open Revit project, start Dynamo, open definition, run definition: all is fine and running.

make another hit on the Run command: Python node returns an exception saying that a transaction is needed…why not the first time?

closing Revit, run again, works at first…weird or logical?

What are you doing in your python node?

CopyElements method. get stuff from linked file and paste in the active document. first try works great, second ask for transaction.