Description of problem:
Nesting ssh sessions from RHEL 7 to RHEL 8 via ssh fails.

Version-Release number of selected component (if applicable):
tmux-2.7-1.el8.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Run tmux on a RHEL 7 system
2. ssh to a RHEL 8 system inside of the tmux session
3. Run any commands that eventually hit the end of the window. Output becomes jumbled and unreadable.

Actual results:
Output is unreadable and only one line is shown

Expected results:
Output continues normally and console is not garbled

Additional info:
The following combinations were tested with the results shown:

• tmux in rhel7 and nested in rhel7, works
• tmux in rhel7 and ssh to rhel7 + tmux, works
• tmux in rhel8 and nested in rhel8, works
• tmux in ubuntu 18.04 and ssh to rhel8 + tmux, works
• tmux in rhel7 and ssh to rhel8+tmux, gets garbled

Both `clear` and `reset` commands do not resolve the issue. The only way that I have been able to resolve it so far is to pull up a man page for any command. When you exit the man page you end up at a blank terminal again, but still, when you hit the buffer or the end of the screen size it is garbled.

Using `tmux refresh` also fixes the screen temporarily until the screen limit is hit again.

I did look at the changelog to see if there is mention about any issues with nested tmux in this way and I don't see anything specific, though obviously there are many updates that are listed as "incompatible changes" and other such messages in the changelog, so I'm not sure if this type of workflow is not support or whether it's expected to work.