• your platform: Linux
• a brief description of the problem with steps to reproduce; split a window into 4 panes, try to merge panel with the one next to it. Essentially "undo" a split.
• your terminal, and $TERM inside and outside of tmux; putty, xterm (outside), screen (inside)

I wish to merge 3 and 4 after 3 was split vertically or otherwise.

| 1 | 2 |
| 3 | 4 |