strange behaviour with Joomla menu and VM categories

[franzpeter]

If linking categories and subcategories into the Joomla main menu it works as long as not using VM categories in the joomla menu with a non existing category inside the  Joomla menu. For example: We have 4 main categories: cameras, furniture, women, men. We create a Joomla main menu, with those four categories so it looks like: Cameras | Furniture | Women | Men and we create links for that four categories choosing VM categories link. Than we create subcategories like digital camera, analog camera within  the Cameras category choosing VM category (not VM categories) for linking. We create subcategories for the Furniture category like chair, table a.s.o. choosing VM category. We decide to add an additional subcategory to the Cameras for example and do use the VM backend, creating a category like mobile phone as another subcategory but do not create a Joomla menu link. It may be a bad example but that could happen for example while importing a lot of categories as subcategories with CSVI or CSVA. So those subcategories are now inside the VM database and the VM category structure but still not linked into the Joomla menu category structure. Those categories get shown by clicking on the main category menu entry for example Cameras. Doing so shows the newly created subcategories because Cameras is linked as VM categories page. If clicking - in the example - on mobile phone - it tries to shows all products. Sometimes that may produce server errors, if crawler try to do so.  All the other subcategories still work, because they are linked inside the menu structure, not so the mobile phone.
Obviously there is a problem when linking with VM categories and than creating a new category in the VM Backend without creating an additional link inside the Joomla menu structure. I do not exactly know why that happens but maybe it has something to do with the way, how VM categories work. Could it be that the subcategories from Virtuemart have a different linking method, maybe a different encoded url (& instead of the Joomla way: & for example). Did see that because I am using such an import tool, which creates categories and products inside VM database, but of course, those categories are still not linked as Joomla menu item after importing.
For now the best way seems to be not using VM categories to link the main categories, instead, -to keep the sef urls-, creating those menu entries only as separators.