nope, this is no ic2 bug , on pack without ic2 i have this :
---- Minecraft Crash Report ----
// I'm sorry, Dave.
Time: 04.09.13 12:38
Description: Exception in server tick loop
java.lang.RuntimeException: java.util.zip.ZipException: Not in GZIP format
at codechicken.enderstorage.api.EnderStorageManager.load(EnderStorageManager.java:157)
at codechicken.enderstorage.api.EnderStorageManager.<init>(EnderStorageManager.java:118)
at codechicken.enderstorage.api.EnderStorageManager.reloadManager(EnderStorageManager.java:195)
at codechicken.enderstorage.api.EnderStorageManager$EnderStorageSaveHandler.onWorldLoad(EnderStorageManager.java:41)
at net.minecraftforge.event.ASMEventHandler_33_EnderStorageSaveHandler_onWorldLoad_Load.invoke(.dynamic)
at net.minecraftforge.event.ASMEventHandler.invoke(ASMEventHandler.java:39)
at net.minecraftforge.event.EventBus.post(EventBus.java:108)
at net.minecraft.server.integrated.IntegratedServer.func_71247_a(IntegratedServer.java:85)
at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:107)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:443)
at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:582)
Caused by: java.util.zip.ZipException: Not in GZIP format
at java.util.zip.GZIPInputStream.readHeader(GZIPInputStream.java:165)
at java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:79)
at java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:91)
at net.minecraft.nbt.CompressedStreamTools.func_74796_a(CompressedStreamTools.java:28)
at codechicken.enderstorage.api.EnderStorageManager.load(EnderStorageManager.java:144)