Problem with files created in Pencil 2 and then opened in Pencil 3

[rusdeveloper]

Files created in Pencil 2 can be opened in Pencil 3 but they behave incorrectly: some objects cannot be edited, some cannot be moved as they are in Pencil 2. Moreover files created in Pencil 2, then opened and saved in Pencil 3 cannot be opened again in Pencil 2. Trying that I get "Error. thiz.doc.pages[p] is undefined".