Today I may have found a bug of the launcher (it may also be the game but I don't know for sure).

I usually have the Minecraft.exe on my C: Drive but I recently changed it to the D: Drive. Since it's on the D: Drive I am not able to allocate more than 512 MB of RAM (When I change back to the C: Drive it's fine).

This is the message of the console...:
--Error occurred during initialization of VM
--Incompatible minimum and maximum heap sizes specified
--Picked up _JAVA_OPTIONS: -Xmx512M

This is the JAVA argument I use to start MC: -Xmx2G -Xms2G
The console output is still the same when changing it to 1G

The Java argument works fine with Mod-Pack-Launchers which are in the same folder...