Sadly I have no savegame. I was running multiple games in parallel so they were overwritten. Since I wasn't participating in the games (7 AIs + passiv player) I don't know what was happening. But at least I can offer a backtrace:



Forcing flag at (64, 104)
Cmd_EnemyFlagAction::execute player(7): flag->owner(8) number=11
Cmd_EnemyFlagAction::execute player(8): flag->owner(7) number=1


Thread 1 "widelands" received signal SIGSEGV, Segmentation fault.
0x000000000119091e in Widelands::Coords::operator== (this=0x48, other=...) at ../src/logic/widelands_geometry.cc:31
31              return x == other.x && y == other.y;

(gdb) bt
#0  0x000000000119091e in Widelands::Coords::operator== (this=0x48, other=...) at ../src/logic/widelands_geometry.cc:31
#1  0x0000000001190973 in Widelands::Coords::operator!= (this=0x48, other=...) at ../src/logic/widelands_geometry.cc:35
#2  0x0000000000dc155a in Widelands::Soldier::battle_update (this=0x99e3ef0, game=...) at ../src/logic/map_objects/tribes/soldier.cc:1257
#3  0x0000000000d58e90 in Widelands::Bob::do_act (this=0x99e3ef0, game=...) at ../src/logic/map_objects/bob.cc:193
#4  0x0000000000d58d5d in Widelands::Bob::act (this=0x99e3ef0, game=..., data=3472) at ../src/logic/map_objects/bob.cc:179
#5  0x0000000000d7736c in Widelands::CmdAct::execute (this=0xc209220, game=...) at ../src/logic/map_objects/map_object.cc:98
#6  0x0000000000e204f9 in Widelands::CmdQueue::run_queue (this=0x7fffffffa090, interval=67, game_time_var=@0x7fffffff9ec8: 19081447) at ../src/logic/cmd_queue.cc:123
#7  0x0000000000d137eb in Widelands::Game::think (this=0x7fffffff9ec0) at ../src/logic/game.cc:555
#8  0x0000000000f34fb5 in InteractiveBase::think (this=0x311fa40) at ../src/wui/interactive_base.cc:306
#9  0x0000000000f48a54 in InteractivePlayer::think (this=0x311fa40) at ../src/wui/interactive_player.cc:169
#10 0x0000000000e9ad13 in UI::Panel::do_think (this=0x311fa40) at ../src/ui_basic/panel.cc:441
#11 0x0000000000e9a5dd in UI::Panel::do_run (this=0x311fa40) at ../src/ui_basic/panel.cc:183
#12 0x0000000000c0c6b6 in UI::Panel::run<UI::Panel::Returncodes> (this=0x311fa40) at ../src/ui_basic/panel.h:96
#13 0x0000000000d134dc in Widelands::Game::run (this=0x7fffffff9ec0, loader_ui=0x7fffffff9e30, start_game_type=Widelands::Game::NewNonScenario, script_to_run="", replay=false,
    prefix_for_replays="single_player") at ../src/logic/game.cc:525
#14 0x0000000000c06ebe in WLApplication::new_game (this=0x18c7690) at ../src/wlapplication.cc:1228
#15 0x0000000000c064b2 in WLApplication::mainmenu_singleplayer (this=0x18c7690) at ../src/wlapplication.cc:1088
#16 0x0000000000c05eb6 in WLApplication::mainmenu (this=0x18c7690) at ../src/wlapplication.cc:994
#17 0x0000000000c02a1e in WLApplication::run (this=0x18c7690) at ../src/wlapplication.cc:441
#18 0x0000000000c010c1 in main (argc=1, argv=0x7fffffffd738) at ../src/main.cc:49



(gdb) display &opponent
9: &opponent = (Widelands::Soldier *) 0x0
(gdb) display battle_
10: battle_ = (Widelands::Battle *) 0xe02cb50
(gdb) display *battle_
11: *battle_ = {<Widelands::MapObject> = {_vptr.MapObject = 0x125b368 <vtable for Widelands::Battle+16>, removed = warning: RTTI symbol not found for class 'boost::signals2::signal<void (unsigned int), boost::signals2::optional_last_value<void>, int, std::less<int>, boost::function<void (unsigned int)>, boost::function<void (boost::signals2::connection const&, unsigned int)>, boost::signals2::mutex>'

{<boost::signals2::signal_base> = {<boost::noncopyable_::noncopyable> = {<No data fields>},
        _vptr.signal_base = 0x1223f28 <vtable for boost::signals2::signal<void (unsigned int), boost::signals2::optional_last_value<void>, int, std::less<int>, boost::function<void (unsignedint)>, boost::function<void (boost::signals2::connection const&, unsigned int)>, boost::signals2::mutex>+16>}, <boost::signals2::detail::std_functional_base<void, unsigned int>> = {<std::unary_function<unsigned int, void>> = {<No data fields>}, <No data fields>}, static arity = <optimized out>, _pimpl = {px = 0xc790d90, pn = {pi_ = 0xf67d860}}},
    descr_ = 0x1899aa0 <Widelands::(anonymous namespace)::g_battle_descr>, serial_ = 354818, logsink_ = 0x0, reserved_by_worker_ = false}, first_ = 0x0, second_ = 0xf507f50,
  creationtime_ = 23928198, readyflags_ = 0 '\000', damage_ = 0, first_strikes_ = true, last_attack_hits_ = 100}



On an earlier autosave an error was reported but I don't think it is related:
"Writing Map Objects ...  Tribe immovable has no owner!!  Tribe immovable has no owner!! took 71ms"