Help with same category sliding

[tokuan]

Need a little help with displaying product in same category slide

When viewing a product in a subcategory with many product, slide is showing other product within this subcategory

problem i am facing is

1. When I click on a product in a subcategory it show this product, and in slide show product in same subcategory, it's ok
2. When I now click on a product in slide, it show product correctly, BUT my slide now show a product from main category,
it's moved one level up. It should show same slide of product in subcategories.

What I don't understand is that for 1 single subcategory it works correctly and other don't?????

correctly link : http://www.siam-trader.com/product.php?id_product=198
error link : http://www.siam-trader.com/product.php?id_product=185, click on slide and slide is in error

Any suggestion for how to solve this problem

Kind Regards
Tom