How do I avoid multiple instances of soffice?

This is on a linux system, Kubuntu 14.04, with LO 5.3. The problem has been around for several versions. If LibreOffice is already running and I open a file from Dolphin, the Application Launcher Documents menu, from an email attachment, a second instance of soffice starts up. System Monitor shows two soffice processes with different PID’s. The second instance thinks the first instance crashed and wants to recover documents that are already open.

What do I need to do so that when I launch documents from outside LibreOffice they open a new window in the already running process instead of starting a new process?