sometimes my Mac fails mounting my Synology DiskStation’s filesystems: “Connection Failed”

• the OS X finder shows: “Connection Failed”
• one of the filesystems (“home”) was mounted beforehand
• it seems impossible to remove that dangling mount point
• all three of my DiskStations seem equally concerned: DS213+, DS112+, DS115j
• I need to reboot the Mac in order to be able to mount any of the filesystems of the concerned DiskStation again – I hate rebooting and losing desktop and application state

Update 2016-01-10:
With cmd-K (“Connect to Server…“) it works rather smoothely – but still not perfectly.