extension files get repeated over and over each time snapcraft is recreated

Every time I modify the gnome.py file from the extensions and rebuild the snap without doing a clean, the size is much bigger. I checked the squashfs and found that the python3.8's build/lib folder is being duplicated each time the snap is rebuilt (as long as the modification date of the file has changed).

I attach a capture where can be seen that in one of the iterations there were four instances of the gnome.py (and the test_gnome.py) file, but after changing one line in gnome.py and rebuilding the snap without doing a clean, there are now five instances.