[SOLVED] Big Sur TextEdit delete line jumps to start of plain text file

When I delete a line in a plain text file in TextEdit on Big Sur (only), the cursor stays in the correct position, but the window scrolls up to the start of the file. I would expect no scrolling to occur.

To reproduce:

create a new file and convert it to plain text
make it 50 lines long. It can have any content, e.g. 1 character per line
reduce the height of the window to 20 lines, to ensure scrolling can be observed
scroll to end of file
use backspace to delete a line or 2 from near the end of the file.

Observed result: window scrolls to the top of the file

Expected result: no scrolling

Is there any workaround, or a setting that can be changed so that this behaviour is not observed?