reported by rgovostes:

If you rename the project while a folder (e.g., the "data" folder) is open,
Processing will rename the PDE file but not the outlying folder.

Consequences include not being able to export the PDE file along with the
rest of your applet.

Preferably, it would check if you have any windows open, and alert you
first, allowing you to close them and continue renaming, or cancel. If you
cancel or there is another problem, it should not rename the PDE file.

suggestion from seltar:

First try to rename the folder, and if works, renamed the file, if it
doesn't work write: "you probably have the project folder open, close that
and try again" in the errormessage that appears..

Because right now, the file gets renamed even though the folder can't be,
and that can get a bit messy..

seems to be specific to windows because of how it handles locking open folders (versus mac
os, who deals with file references separately from the actual paths).