I set up Lightzone as an external editor in prefs.  I select a couple of photos to edit in lightzone and I am only able to get one photo out of selection to open up in LZ.  I am selected the option of "editing selected images".  I have a request in with LZ also because I'm not sure it's  an issue with them or PM.
Thanks
macbook air 11"
os 10.11.4
pm  hoto Mechanic Version 5.0, build 17719 (c8049ca)