Ok, I found out that the minetest.conf doesn't get created until a world is played, so now I have a minetest.conf file to configure. Here is the debugging level four for my system when this crash happens...
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08:15:02: INFO[main]: logfile = /home/scott/.minetest/debug.txt
08:15:02: VERBOSE[main]: httpfetch_init: parallel_limit=8
08:15:02: INFO[main]: Message locale is now set to: LC_CTYPE=en_US.UTF-8;LC_NUMERIC=C;LC_TIME=en_US.UTF-8;LC_COLLATE=en_US.UTF-8;LC_MONETARY=en_US.UTF-8;LC_MESSAGES=en_US.UTF-8;LC_PAPER=en_US.UTF-8;LC_NAME=en_US.UTF-8;LC_ADDRESS=en_US.UTF-8;LC_TELEPHONE=en_US.UTF-8;LC_MEASUREMENT=en_US.UTF-8;LC_IDENTIFICATION=en_US.UTF-8
08:15:02: INFO[main]: text_height=16
08:15:02: INFO[main]: Searching worlds...
08:15:02: INFO[main]: In /home/scott/.minetest/worlds:
08:15:02: INFO[main]: sad
08:15:02: INFO[main]: 1 found.
08:15:02: INFO[main]: Waiting for other menus
08:15:02: INFO[main]: Waited for other menus
08:15:02: INFO[main]: Audio: Initializing...
08:15:02: INFO[main]: Audio: Vorbis extension NOT present
08:15:02: INFO[main]: Audio: Initialized: OpenAL 1.1 ALSOFT 1.14, using OpenAL Soft
08:15:02: INFO[main]: GUIEngine: Initializing Lua
08:15:02: INFO[AsyncWorkerThread_0]: Initializing Asynchronous environment
08:15:02: INFO[AsyncWorkerThread_1]: Initializing Asynchronous environment
08:15:02: INFO[AsyncWorkerThread_2]: Initializing Asynchronous environment
08:15:02: INFO[main]: SCRIPTAPI: initialized mainmenu modules
08:15:02: VERBOSE[main]: Loading and running script from /usr/share/games/minetest/builtin/mainmenu.lua
08:15:02: INFO[main]: Searching worlds...
08:15:02: INFO[main]: In /home/scott/.minetest/worlds:
08:15:02: INFO[main]: sad
08:15:02: INFO[main]: 1 found.
08:15:02: INFO[AsyncWorkerThread_3]: Initializing Asynchronous environment
08:15:02: VERBOSE[main]: OpenALSoundManager::maintain(): 0 playing sounds, 0 sound names loaded
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.0.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.1.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.2.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.3.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.4.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.5.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.6.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.7.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.8.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.9.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /home/scott/.minetest/sounds/main_menu.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.0.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.1.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.2.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.3.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.4.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.5.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.6.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.7.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.8.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.9.ogg for decoding
08:15:02: INFO[main]: Audio: Error opening /usr/share/games/minetest/sounds/main_menu.ogg for decoding
08:15:02: INFO[main]: OpenALSoundManager: "main_menu" not found.
08:15:26: INFO[main]: GUIFormSpecMenu: Not allowing focus change.
I'll repeat my system details so you all don't have to search my prior posts in this thread for them ;) . This machine is an hp laptop with 32 bit ubuntu 14.04 (although I had the crash with 64 bit ubuntu 14.04 also). The version of minetest is 0.4.9 from the ubuntu software center. The bug is definitely reproducible, since it happens every time I select the client tab of minetest and then select the public server list box. I hope this helps.