Pcbnew: differential router unable to commit segment, double click cancels the routing action when "DP Gap" smaller less than "Clearance" value

Description

When tweaking the differential routing values for a net class, the router seems to break if the value for "DP Gap" is smaller than the value set in "Clearance". The router will start a new trace, but can't commit segments and double clicking ends the action. This is undesired/unexpected, since the gap should be set according to impedance calculations while clearance would be something like four times the line width to avoid cross talk, which is a larger value.

Steps to reproduce

1. Have components with diff traces on a board
2. Open Board Setup -> Net Classes -> set "DP Gap" for the Default net to something smaller than the value in "Clearance"
3. Try and route traces

KiCad Version

Application: Pcbnew
Version: (5.99.0-2318-gf1aa7e523), release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.64.1 SecureTransport (LibreSSL/2.8.3) zlib/1.2.11 nghttp2/1.39.2
Platform: macOS Catalina Version 10.15.5 (Build 19F101), 64 bit, Little endian, wxMac
Build Info:
    Date: Jul 16 2020 06:46:57
    wxWidgets: 3.0.4 (wchar_t,STL containers,compatible with 2.8)
    Boost: 1.72.0
    OCE: 6.9.1
    Curl: 7.54.0
    ngspice: 31
    Compiler: Clang 10.0.1 with C++ ABI 1002
Build settings:
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=OFF
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=OFF
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_SPICE=ON