Creating new tmux tabs shortens window height each time

1. I start a tmux session in an iTerm 2 window using ssh -A -t hermes "tmux -CC attach || tmux -CC".

2. Each time I press Command-T, the new tab is one line shorter than the previous one. This happens for every subsequent new tab.

This is a new behavior with the latest update. Also, new windows start out two lines shorten than they used to.