ncurses 6.1 crashes tmux when starting simple term (st)

[Max Zhao]

Hello,

I am using Archlinux x64 (4.15.5-1). After upgrading ncurses to 6.1 it 
has caused tmux sessions to crash when starting neovim. This only occurs 
when using tmux inside of simple-term. Other terminals such as kitty or 
xfce-terminal are not affected.

Reverting ncurses to 6.0 actually fixes the issue.

I have also described the bug here: 
https://bbs.archlinux.org/viewtopic.php?id=234699

The issue can be reproduced by starting neovim inside of a tmux session 
using simple-term.

Any help in debugging this issues would be greatly appreciated.

Best regards,

Max