I am making a library mod to make making my mods easier and I added a test module including a test potion. When I tested it, the effect continued working even after it ran out of time.

BasicPotion:

Spoiler

package drmeepster.drcorester.potion;

import drmeepster.drcorester.property.PropertyHandler;
import drmeepster.drcorester.util.IBasicObject;
import net.minecraft.client.Minecraft;
import net.minecraft.client.gui.Gui;
import net.minecraft.entity.EntityLivingBase;
import net.minecraft.potion.Potion;
import net.minecraft.potion.PotionEffect;
import net.minecraft.util.ResourceLocation;
import net.minecraftforge.fml.relauncher.Side;
import net.minecraftforge.fml.relauncher.SideOnly;

public abstract class BasicPotion extends Potion implements IBasicObject<Potion>{
    
    //copy these
    //public static final String NAME = "";
    //public static final int COLOR = 0x000000;
    
    private ResourceLocation icon;
    private String id;

    protected BasicPotion(boolean isBad, int color, String name, String modid) {
        super(true, color);
        this.setPotionName("effect." + PropertyHandler.getName(modid, name));
        this.setRegistryName(modid, name);
        this.setIconIndex(0, 0);
        icon = new ResourceLocation(modid, "textures/potion/" + name + ".png");
        System.out.println(icon);
        id = name;
    }
    
    @Override
    public boolean isReady(int duration, int amplifier){
        return true;
    }
    
    @Override
    public boolean hasStatusIcon(){
        return false;
    }
    
    @SideOnly(Side.CLIENT)
    @Override
    public void renderInventoryEffect(int x, int y, PotionEffect effect, Minecraft mc) {
        if (mc.currentScreen != null) {
            mc.getTextureManager().bindTexture(icon);
            Gui.drawModalRectWithCustomSizedTexture(x + 6, y + 7, 0, 0, 18, 18, 18, 18);
        }
    }
    
    @SideOnly(Side.CLIENT)
    @Override
    public void renderHUDEffect(int x, int y, PotionEffect effect, net.minecraft.client.Minecraft mc, float alpha){
        mc.getTextureManager().bindTexture(icon);
        Gui.drawModalRectWithCustomSizedTexture(x + 3, y + 3, 0, 0, 18, 18, 18, 18);
    }
    
    @Override
    public String getId(){
        return id;
    }
    
    /* Copy this:
     * public void performEffect(EntityLivingBase entity, int amplifier){
     */
}

PotionTest:

Spoiler

package drmeepster.drcorester.testing;

import drmeepster.drcorester.ModDrCorester;
import drmeepster.drcorester.potion.BasicPotion;
import net.minecraft.entity.EntityLivingBase;

public class PotionTest extends BasicPotion {

    public static final String NAME = "potion_test";
    public static final int COLOR = 0x000000;
    
    protected PotionTest() {
        super(false, COLOR, NAME, ModDrCorester.MODID);
    }
    
    @Override
    public void performEffect(EntityLivingBase entity, int amplifier){
        entity.setFire(1);
    }
}
 

 

??????? I commented out the line that sets the player on fire and uncommented it and it started working.