SUMMARY
Creating a document with python creates a broken document.

STEPS TO REPRODUCE
1. with a new instance of Krita
2. run the code given to create a new document
3. draw on the canvas (nothing is seen when drawing)
4. toggle isolate layer (to see drawing)
5. toggle isolate layer again (to hide drawing)

"""
import krita

# Create a Document
newDocument = Krita.instance().createDocument(1920, 1080, "name", "RGBA", "U8", "", 300.0)
Krita.instance().activeWindow().addView(newDocument)
"""

OBSERVED RESULT
it will create a transparent document event though there is a white background.
On step 3  drawing will happen but it is not shown despite the isolate layer state being off.
Activating isolate layer state will in reality deactivate it and show the drawing and you can verify this by swapping between isolate layer state on and off.

EXPECTED RESULT
Create a empty document and see the while background as normal, and when activating or deactivating isolate layer should give the same display because there is only one layer present.

SOFTWARE/OS VERSIONS
Windows: 10
Qt Version: 5.12.12

ADDITIONAL INFORMATION
Saving this document will remain broken on file when loading up I believe.