Memory Leak when using HD Textures

When using an HD Texture pack with a resolution higher than 64x64, one begins to experience serious FPS drop. When using a texture pack with a resolution higher than 256x256, the game will freeze and/or finally spit out this error:

java.lang.OutOfMemoryError: Direct buffer memory
at java.nio.Bits.reserveMemory(Bits.java:632)
at java.nio.DirectByteBuffer.<init>(DirectByteBuffer.java:97)
at java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:288)
at bii.a(SourceFile:395)
at bii.<init>(SourceFile:135)
at bii.<init>(SourceFile:107)
at bik.a(SourceFile:127)
at bik.c(SourceFile:100)
at bil.b(SourceFile:80)
at bfy.d(SourceFile:350)
at bfy.c(SourceFile:301)
at bjr.a(SourceFile:146)
at axn.a(SourceFile:175)
at bjq.a(SourceFile:109)
at bfk.b(SourceFile:768)
at net.minecraft.client.Minecraft.K(SourceFile:595)
at net.minecraft.client.Minecraft.run(SourceFile:524)
at java.lang.Thread.run(Thread.java:662)

(Memory at that points hits around 220,000K, approximately 6GB of RAM was being used at that moment)