string-rectangle provides on-the-fly preview, undesirably

[Bob Proulx]

The command C-x r t string-rectangle in version 24 and previously
would "Replace rectangle contents with STRING on each line
(‘string-rectangle’)."  The same happens in version 25 but
differently.  In version 25 the change is displayed incrementally
character by character as you type.  With a large displayed rectangle
this can cause a lot of dynamic "flicker" as every character on the
display is moved.  This is driving me crazy.

Is there a way to return to the previous version 24 behavior?

Thanks,
Bob

P.S. The NEWS file says:

*** 'string-rectangle' provides on-the-fly preview of the result.