GuiSlot not calling drawSlot

I'm having a problem where my drawSlot method is not being called in my GuiRewardsList that extends GuiSlot. Here is the relevant code:

GuiVote (the parent GUI):

package me.superckl.VoltzationCore.client;

import net.minecraft.client.gui.GuiButton;
import net.minecraft.client.gui.GuiScreen;
import net.minecraft.client.gui.GuiSlot;
import net.minecraft.client.gui.inventory.GuiContainer;

import org.lwjgl.opengl.GL11;

public class GuiVote extends GuiScreen{

private final GuiRewardList list;

public GuiVote() {
	this.list = new GuiRewardList(this, this.fontRenderer);
}

@Override
public void initGui() {
	//TODO add buttons and such here
}


@Override
protected void actionPerformed(final GuiButton par1GuiButton) {
	//TODO called when a button is clicked
}

@Override
public void updateScreen() {
	//TODO If vote while open, change to thank you
}

@Override
public void drawScreen(int par1, int par2, float par3){
	// TODO refer to following code, drawn before items
	this.drawDefaultBackground();
	GL11.glColor4f(1.0F, 1.0F, 1.0F, 1.0F);
	this.mc.renderEngine.bindTexture("/mods/voltzationcore/textures/gui/vote.png");
	final int k = (this.width - 176) / 2;
	final int l = (this.height - 166) / 2;
	this.drawTexturedModalRect(k, l, 0, 0, 176, 166);
	this.list.drawScreen(par1, par2, par3);
	super.drawScreen(par1, par2, par3);
}

}

GuiRewardsList:

package me.superckl.VoltzationCore.client;

import net.minecraft.client.Minecraft;
import net.minecraft.client.gui.FontRenderer;
import net.minecraft.client.gui.GuiScreen;
import net.minecraft.client.gui.GuiSlot;
import net.minecraft.client.renderer.Tessellator;

public class GuiRewardList extends GuiSlot{

private final GuiVote gui;
private final FontRenderer font;

public GuiRewardList(GuiVote gui, FontRenderer font) {
	super(Minecraft.getMinecraft(), gui.width, gui.height, 32, gui.height, 20);
	this.gui = gui;
	this.font = font;
}

@Override
protected int getSize() {
	// TODO Auto-generated method stub
	return 1;
}

@Override
protected void elementClicked(int i, boolean flag) {
	// TODO Auto-generated method stub

}

@Override
protected boolean isSelected(int i) {
	// TODO Auto-generated method stub
	return false;
}

@Override
public int getContentHeight(){
	return 20;
}

@Override
public void drawScreen(int i, int j, float k){
        //this.font.setBidiFlag(true);
        //this.gui.drawCenteredString(this.font, "testing 123", this.gui.width / 2, this.gui.height/2, 0x19ee37);
	System.out.println("Drawing Screen");
        super.drawScreen(i, j, k);
}

@Override
protected void drawSlot(int par1, int par2, int par3, int par4, Tessellator tessellator) {
        this.font.setBidiFlag(true);
        this.gui.drawCenteredString(this.font, "testing 123", this.gui.width / 2, this.gui.height/2, 0x19ee37);
        System.out.println("DREW THE STRING!");
}

@Override
protected void drawBackground() {
	// TODO Auto-generated method stub
	System.out.println("Drawing background");
}

}

In the GuiSlot class, drawBackground and drawScreen are being called, since the logs are being printed (about 20 times a second, obviously). But, the drawSlot method is not called once. Does it have something to do with my positioning or is there something wrong that's deeper?

Thanks for any help.