I have had problems with SubEthaEdit making Max/MSP .mxo externals show up as folders instead of packages. I type the solution here so that I won’t get forget it anymore (thanks to jasch for figuring this out):

  1. Right click on SubEthaEdit and select “show package contents”
  2. Open the Info.plist file in a text editor
  3. Remove the line with mxo
  4. Save and restart