When I "tear off" (detach) multiple editor windows in Eclipse, content assist (autocompletion) causes a "Next Editor" transition. I'm using the Java editor.
I've looked through all of the relevant Preferences and Key Bindings, but I haven't found anything which affects this behavior.
Eclipse version info:
Version: Luna Service Release 1a (4.4.1) Build id: 20150109-0600
My environment is not heavily customized, so I'm surprised to not see others running into this.
Gary