Bug#860789: freecad: import of openscad file turns "differences" into "unions"

[lkcl]

Package: freecad
Version: 0.16+dfsg2-3
Severity: normal
Tags: upstream

in attempting to convert from OpenSCAD to STEP,
found the advice here and followed it:
https://forum.lulzbot.com/viewtopic.php?t=243

however the following file has all of its "difference" (removal)
objects turned into "unions" (additions):
http://hands.com/~lkcl/microdesktop_prog2.scad



-- System Information:
Debian Release: 7.4
  APT prefers testing
  APT policy: (500, 'testing'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.9.0-1-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages freecad depends on:
ii  libboost-atomic1.62.0           1.62.0+dfsg-4
ii  libboost-chrono1.62.0           1.62.0+dfsg-4
ii  libboost-date-time1.62.0        1.62.0+dfsg-4
ii  libboost-filesystem1.62.0       1.62.0+dfsg-4
ii  libboost-program-options1.62.0  1.62.0+dfsg-4
ii  libboost-python1.62.0           1.62.0+dfsg-4
ii  libboost-regex1.62.0            1.62.0+dfsg-4
ii  libboost-signals1.62.0          1.62.0+dfsg-4
ii  libboost-system1.62.0           1.62.0+dfsg-4
ii  libboost-thread1.62.0           1.62.0+dfsg-4
ii  libc6                           2.23-4
ii  libcoin80v5                     3.1.4~abc9f50+dfsg1-1
ii  libfreeimage3                   3.17.0+ds1-1.1+b1
ii  libfreetype6                    2.6.3-3+b1
ii  libgcc1                         1:6.3.0-10
ii  libgl1-mesa-glx [libgl1]        13.0.6-1
ii  libglu1-mesa [libglu1]          9.0.0-2.1
ii  liboce-foundation10             0.17.2-1
ii  liboce-modeling10               0.17.2-1
ii  liboce-ocaf-lite10              0.17.2-1
ii  liboce-ocaf10                   0.17.2-1
ii  liboce-visualization10          0.17.2-1
ii  libpyside1.2                    1.2.2-2+b1
ii  libpython2.7                    2.7.13-1
ii  libqt4-network                  4:4.8.6+git64-g5dc8b2b+dfsg-2+b1
ii  libqt4-opengl                   4:4.8.6+git64-g5dc8b2b+dfsg-2+b1
ii  libqt4-svg                      4:4.8.6+git64-g5dc8b2b+dfsg-2+b1
ii  libqt4-xml                      4:4.8.6+git64-g5dc8b2b+dfsg-2+b1
ii  libqtcore4                      4:4.8.6+git64-g5dc8b2b+dfsg-2+b1
ii  libqtgui4                       4:4.8.6+git64-g5dc8b2b+dfsg-2+b1
ii  libqtwebkit4                    2.3.4.dfsg-3
ii  libshiboken1.2v5                1.2.2-2+b2
ii  libsoqt4-20                     1.6.0~e8310f-2+b1
ii  libspnav0                       0.2.3-1
ii  libstdc++6                      6.3.0-10
ii  libx11-6                        2:1.6.4-3
ii  libxerces-c3.1                  3.1.1-5
ii  libxext6                        2:1.3.3-1+b2
ii  libzipios++0v5                  0.1.5.9+cvs.2007.04.28-5.2
ii  pyside-tools                    0.2.15-1
ii  python-collada                  0.4-2
ii  python-matplotlib               2.0.0~rc2-1
ii  python-pivy                     0.5.0~v609hg-3.1
ii  python-ply                      3.9-1
ii  python-pyside                   1.2.2-2
ii  python2.7                       2.7.13-1
pn  python:any                      <none>
ii  zlib1g                          1:1.2.8.dfsg-2+b1

freecad recommends no packages.

Versions of packages freecad suggests:
ii  graphviz  2.38.0-16
pn  povray    <none>

-- no debconf information