Henri D

It is not a duplicate since the arguments "-DsocksProxyHost=localhost -DsocksProxyPort=5678" work until 13w39b.

Moreover, it is not a launcher issue since minecraft (the game) is run with the correct arguments.
The only thing that change is the Minecraft version.
And, I can reproduce the issue without the launcher using either --proxyPort --proxyHost or -DsocksProxyPort/Host :

/usr/lib/jvm/java-7-openjdk/jre/bin/java -DsocksProxyHost=localhost -DsocksProxyPort=5678 -Xmx1G -Djava.library.path=/home/riri/.minecraft/versions/1.7.2/1.7.2-natives-3273057565428 -cp /home/riri/.minecraft/libraries/java3d/vecmath/1.3.1/vecmath-1.3.1.jar:/home/riri/.minecraft/libraries/net/sf/trove4j/trove4j/3.0.3/trove4j-3.0.3.jar:/home/riri/.minecraft/libraries/com/ibm/icu/icu4j-core-mojang/51.2/icu4j-core-mojang-51.2.jar:/home/riri/.minecraft/libraries/net/sf/jopt-simple/jopt-simple/4.5/jopt-simple-4.5.jar:/home/riri/.minecraft/libraries/com/paulscode/codecjorbis/20101023/codecjorbis-20101023.jar:/home/riri/.minecraft/libraries/com/paulscode/codecwav/20101023/codecwav-20101023.jar:/home/riri/.minecraft/libraries/com/paulscode/libraryjavasound/20101123/libraryjavasound-20101123.jar:/home/riri/.minecraft/libraries/com/paulscode/librarylwjglopenal/20100824/librarylwjglopenal-20100824.jar:/home/riri/.minecraft/libraries/com/paulscode/soundsystem/20120107/soundsystem-20120107.jar:/home/riri/.minecraft/libraries/io/netty/netty-all/4.0.10.Final/netty-all-4.0.10.Final.jar:/home/riri/.minecraft/libraries/com/google/guava/guava/15.0/guava-15.0.jar:/home/riri/.minecraft/libraries/org/apache/commons/commons-lang3/3.1/commons-lang3-3.1.jar:/home/riri/.minecraft/libraries/commons-io/commons-io/2.4/commons-io-2.4.jar:/home/riri/.minecraft/libraries/net/java/jinput/jinput/2.0.5/jinput-2.0.5.jar:/home/riri/.minecraft/libraries/net/java/jutils/jutils/1.0.0/jutils-1.0.0.jar:/home/riri/.minecraft/libraries/com/google/code/gson/gson/2.2.4/gson-2.2.4.jar:/home/riri/.minecraft/libraries/com/mojang/authlib/1.3/authlib-1.3.jar:/home/riri/.minecraft/libraries/org/apache/logging/log4j/log4j-api/2.0-beta9/log4j-api-2.0-beta9.jar:/home/riri/.minecraft/libraries/org/apache/logging/log4j/log4j-core/2.0-beta9/log4j-core-2.0-beta9.jar:/home/riri/.minecraft/libraries/org/lwjgl/lwjgl/lwjgl/2.9.0/lwjgl-2.9.0.jar:/home/riri/.minecraft/libraries/org/lwjgl/lwjgl/lwjgl_util/2.9.0/lwjgl_util-2.9.0.jar:/home/riri/.minecraft/versions/1.7.2/1.7.2.jar net.minecraft.client.main.Main --username nheir --version 1.7.2 --gameDir /home/riri/.minecraft --assetsDir /home/riri/.minecraft/assets  --accessToken 1

/usr/lib/jvm/java-7-openjdk/jre/bin/java -Xmx1G -Djava.library.path=/home/riri/.minecraft/versions/1.7.2/1.7.2-natives-3273057565428 -cp /home/riri/.minecraft/libraries/java3d/vecmath/1.3.1/vecmath-1.3.1.jar:/home/riri/.minecraft/libraries/net/sf/trove4j/trove4j/3.0.3/trove4j-3.0.3.jar:/home/riri/.minecraft/libraries/com/ibm/icu/icu4j-core-mojang/51.2/icu4j-core-mojang-51.2.jar:/home/riri/.minecraft/libraries/net/sf/jopt-simple/jopt-simple/4.5/jopt-simple-4.5.jar:/home/riri/.minecraft/libraries/com/paulscode/codecjorbis/20101023/codecjorbis-20101023.jar:/home/riri/.minecraft/libraries/com/paulscode/codecwav/20101023/codecwav-20101023.jar:/home/riri/.minecraft/libraries/com/paulscode/libraryjavasound/20101123/libraryjavasound-20101123.jar:/home/riri/.minecraft/libraries/com/paulscode/librarylwjglopenal/20100824/librarylwjglopenal-20100824.jar:/home/riri/.minecraft/libraries/com/paulscode/soundsystem/20120107/soundsystem-20120107.jar:/home/riri/.minecraft/libraries/io/netty/netty-all/4.0.10.Final/netty-all-4.0.10.Final.jar:/home/riri/.minecraft/libraries/com/google/guava/guava/15.0/guava-15.0.jar:/home/riri/.minecraft/libraries/org/apache/commons/commons-lang3/3.1/commons-lang3-3.1.jar:/home/riri/.minecraft/libraries/commons-io/commons-io/2.4/commons-io-2.4.jar:/home/riri/.minecraft/libraries/net/java/jinput/jinput/2.0.5/jinput-2.0.5.jar:/home/riri/.minecraft/libraries/net/java/jutils/jutils/1.0.0/jutils-1.0.0.jar:/home/riri/.minecraft/libraries/com/google/code/gson/gson/2.2.4/gson-2.2.4.jar:/home/riri/.minecraft/libraries/com/mojang/authlib/1.3/authlib-1.3.jar:/home/riri/.minecraft/libraries/org/apache/logging/log4j/log4j-api/2.0-beta9/log4j-api-2.0-beta9.jar:/home/riri/.minecraft/libraries/org/apache/logging/log4j/log4j-core/2.0-beta9/log4j-core-2.0-beta9.jar:/home/riri/.minecraft/libraries/org/lwjgl/lwjgl/lwjgl/2.9.0/lwjgl-2.9.0.jar:/home/riri/.minecraft/libraries/org/lwjgl/lwjgl/lwjgl_util/2.9.0/lwjgl_util-2.9.0.jar:/home/riri/.minecraft/versions/1.7.2/1.7.2.jar net.minecraft.client.main.Main --username nheir --version 1.7.2 --gameDir /home/riri/.minecraft --assetsDir /home/riri/.minecraft/assets --accessToken 1  --proxyHost localhost --proxyPort 5678

Minecraft 1.7.2 does not take into account the proxy settings.
Plus 13w39b (and previous) uses -DsocksProxyHost/Port but ignores --proxyHost/Port.