Parent/Child product makes some other products to disappear

[kosijer]

I'm administrating the shop with more than 3000 products. Few days ago I've added the product with its child products that appeared properly with nice drop-down list that works absolutely fantastic.

Then, I realised that some other categories become empty. That happened only with categories with more than 170-172 products inside.
If I split these categories in smaller parts (less than 170), all products reappear).

Is there anybody who had some similar issue?