ERC does not find unconnected Power Ports (lp:#1639400)

Original report created by David Pearce (halzia)

Eeschema bug
Power Ports have a "Pin" like a component symbol, but ERC does not flag if
the Power Port is not attached to a wire segment. The consequence is that a
Power Port can be placed on a wire and fail to name the net correctly,
resulting islands of isolated tracks.
The attached screenshot shows an "orphan" Power Port and an unconnected
resistor. The resistor IS detected by ERC

Application: kicad
Version: 4.0.4-stable release build
wxWidgets: Version 3.0.2 (debug,wchar_t,compiler with C++ ABI 1009,GCC
5.2.0,wx containers,compatible with 2.8)
Platform: Windows 7 (build 7601, Service Pack 1), 64-bit edition, 64 bit,
Little endian, wxMSW
Boost version: 1.57.0
         USE_WX_GRAPHICS_CONTEXT=OFF
         USE_WX_OVERLAY=OFF
         KICAD_SCRIPTING=ON
         KICAD_SCRIPTING_MODULES=ON
         KICAD_SCRIPTING_WXPYTHON=ON
         USE_FP_LIB_TABLE=HARD_CODED_ON
         BUILD_GITHUB_PLUGIN=ON

Original tags: eeschema erc