I was having this same problem. I tried starting the launcher in compatibility mode for Windows XP SP3, and that solved the problem. I don't know how, but it works.
Think it will, I think the issue emanates from the launcher, can you check it if it sill happens with the magic launcher? http://www.minecraft...s-options-news/
Or any other launcher for that matter.
Because I can't repeat the issue, with my system (or VM's)
I'm having the same problem. I've had 5 instances of javaw.exe running at the same time. I'm opening Minecraft with the vanilla launcher and am using Windows 7 64-bit.
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http://www.minecraftforum.net/topic/1405977-minecrafts-java-process-will-not-die-on-closure-or-at-all-for-that-matter/
This person is having the same problem with the magic launcher, so that's not the problem.
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