Environment

Windows build number: [run `[Environment]::OSVersion` for powershell, or `ver` for cmd] next (19613.1000).
Windows Terminal version (if applicable): Inbox console

Any other software? NVDA

Steps to reproduce

1. Download this list of domains.

2. Start Windows Console and NVDA (with UIA in Windows Console enabled in advanced preferences).

3. Run a python interpreter: python.

4. Run:

   fin=open("domains.txt")
   fin.readlines()

Expected behaviour

Like in pre-21H1 conhost and Windows Terminal 0.11, NVDA reads current output immediately.

Actual behaviour

At this point, NVDA's auto-read lags far behind the actual output in the buffer. Quitting Python with quit() continues reading very old output.

Context

When a text change event is received, NVDA takes a diff of the old and new text and reads only the changed portion of the text. Maybe there's a bug in our diffing algorithm (implemented here, in LiveText._calculateNewText)?