Problem with transfer progress bar

In the serial port link, when using the lrzsz tool to send from the computer to the target device, the progress bar will instantly display to 99%, like this:

The report identifies the serial port link and lrzsz transfer from a computer to a target device; begin by reproducing that transfer and observing the progress updates. Done means the bar reflects transfer progress instead of jumping immediately to 99%, with the behavior verified during a complete send.

Written by the indexing model from the issue text.