Crash when changing footprint editor parameters on macOS

Reproduction steps:

1. Create new project or open an empty project
2. Open the Footprint Editor
3. Click on 'New footprint using footprint wizard'
4. Click on 'Select wizard script to run'
5. Pick QFN
6. Click on the "EPad" label on the left side.
7. Click twice on the "epad" checkbox, to get it to an unticked state.
8. Select the 'Pads' label on the left side. Crash occurs (see attachment for stack trace).

System version information:

ProductName: Mac OS X
ProductVersion: 10.13.3
BuildVersion: 17D102

KiCad version information:

Packaged on 20180309-033023
KiCad revision: r9c62792
KiCad CMake Settings: -DDEFAULT_INSTALL_PATH=/Library/Application Support/kicad
-DCMAKE_C_COMPILER=/usr/bin/clang
-DCMAKE_CXX_COMPILER=/usr/bin/clang++
-DCMAKE_OSX_SYSROOT=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk
-DCMAKE_OSX_DEPLOYMENT_TARGET=10.9
-DwxWidgets_CONFIG_EXECUTABLE=../wx/wx-bin/bin/wx-config
-DKICAD_SCRIPTING=ON
-DKICAD_SCRIPTING_MODULES=ON
-DKICAD_SCRIPTING_WXPYTHON=ON
-DKICAD_SCRIPTING_ACTION_MENU=ON
-DPYTHON_EXECUTABLE=/usr/bin/python
-DPYTHON_SITE_PACKAGE_PATH=/Volumes/SSD/workspace/osx-kicad-adam-head/wx/wx-bin/lib/python2.7/site-packages
-DKICAD_USE_OCE=ON
-DOCE_DIR=/Users/kicad/homebrew/opt/oce/OCE.framework/Versions/0.17/Resources/
-DKICAD_SPICE=ON
-DKICAD_REPO_NAME=maser-c4osx
-DCMAKE_INSTALL_PREFIX=../bin
-DCMAKE_BUILD_TYPE=RelWithDebInfo
Build script revision: r9c62792

Thank you for your time,
Alessandro