White line appears when in full-screen

• iTerm2 version: Build 3.4.0beta11
• OS version: macOS 11 Big Sur Beta (20A5395g)
• plist File: com.googlecode.iterm2.plist
• Video capture of the behavior: Screen_Recording_2020-10-19_at_9.58.57_AM

Detailed steps to reproduce the problem:

1. Open iTerm2
2. Hit Command+Enter to enter full-screen
3. Type normally

What happened:

As I type in full-screen, I periodically see a white line at the top of the screen. When the line appears, it will remain until I type the next character. I have a black background so its pretty obvious when it happens. When running tmux, the line is slightly smaller in height, but still appears. There is no shift in the position of the text on screen when this occurs.

What should have happened:

The background should remain the normal background color.