Hmm will try to sort this out. (keep you guys posted)
Only the weird thing is it when disable www(.)motorkampeerwinkel(.)nl/branders-en-benodigdheden?product_id=361 the product what is showing as a complet productpage on the layout is also gone. the product that is disabled is only behaving the "little malfunction"
There may be a lot of formatting issues or multi-line code from multiple items causing this. Sometimes, it's very hard to find out exactly which item it is so you have to play around with disabling different ones or blocks to clean it up (it may not be the last item).
I imported over 800 items and ran into probably 50 of these since the data I had was altered a bit (I had to delete the bottom section of the description) so a lot of code problems overall.
I then used a unix script to search for the number (count of things like <div> </div>, etc) to make sure they matched. After cleaning it up, the problem went away.
Takes a lot time and data cleaning is a bitch to deal with...especially if you have hundreds or thousands of items to do.