[Bug] Scroll wraparound problem

[rw-van]

After running a program that produced a lot of output, the end of the log was visible, and the prompt was showing.
There was no scroll bar visible.
Using the scroll wheel, I attempted to scroll back through the log.
On scrolling a single line, text was inserted in the middle of the log, pushing the prompt down off the screen, but pushing the upper part of the display up.
After typing control-C a few times, additional prompts were showing. Scrolling a single line would make the prompts immediately disappear.
The attached images are:

• Before scrolling
• One click on the scroll wheel, which should scroll up one line
• Second click on the scroll wheel, which should scroll up a second line