When you zoom a level out as far as possible and then open the replay editor, you cannot move the mouse cursor to the close button, due to the screen being too far zoomed out. This really should be fixed.
Thanks. Will look into this.
Disable mouse capture before opening replay editor, re-enable it when done.
This bug will most likely also affect the options menu, now that it's available in game.
Workaround until fixed: Use Enter (for OK) or Esc (for cancel) to exit those menus.
I just implemented a bug-fix for this, that will be contained in the next new-formats NeoLemmix update.