Apparently it was not a bug, the :- and :+ keys must appear in the same map:
{:- {:editor {"pmeta-shift-s" [:save-as]}}
:+ {:app {"pmeta-shift-s" [:save-all]}
:editor {"alt-w" [:editor.watch.watch-selection]
"alt-shift-w" [:editor.watch.unwatch]
"f3" [:find.next]}
:tabs {"pmeta-pagedown" [:tabs.next]
"pmeta-pageup" [:tabs.prev]}}}}