First of all, they show up perfectly fine in the Eclipse test environment:

 

 

But when I compile the mod and go into normal single-player they're just not there:

 

 

They clearly are all in that tab:

 

bluePot = new com.pixelmoncore.blocks.EntityBluePot().setCreativeTab(tabPixelmonCoreDecoration).setBlockName("bluePot");
GameRegistry.registerBlock(bluePot, "bluePot");
brownPot = new com.pixelmoncore.blocks.EntityBrownPot().setCreativeTab(tabPixelmonCoreDecoration).setBlockName("brownPot");
GameRegistry.registerBlock(brownPot, "brownPot");
PC = new com.pixelmoncore.blocks.EntityPC().setCreativeTab(tabPixelmonCoreDecoration).setBlockName("PC");
GameRegistry.registerBlock(PC, "PC");
Plant = new com.pixelmoncore.blocks.EntityPlant().setCreativeTab(tabPixelmonCoreDecoration).setBlockName("plant");
GameRegistry.registerBlock(Plant, "Plant");
CuttingBoard = new com.pixelmoncore.blocks.EntityCuttingBoard().setCreativeTab(tabPixelmonCoreDecoration).setBlockName("cuttingboard");
GameRegistry.registerBlock(CuttingBoard, "CuttingBoard");
Skillet = new com.pixelmoncore.blocks.EntitySkillet().setCreativeTab(tabPixelmonCoreDecoration).setBlockName("skillet");
GameRegistry.registerBlock(Skillet, "Skillet");

 

So why don't they show up after compiling??

No one has any ideas? :L

Are your models in assets?  Are you sure the assets are exported properly (into correct locations in resulting jar)?  Do you see any console errors related to the models?

 

Also, it seems to be worse that just not showing the models, it doesn't even have a space for them.  To me that means that the item itself isn't registered to the tab.  I know your code and your Eclipse testing shows that they do work, but obviously something is wrong in the exported version.

 

I would add debug console statements to the constructors of those items to confirm that they are indeed being created.  You may want to print out all the items in the game in the postInit() portion of the FML life cycle, to confirm that they are there.