Problem with category association in BO

[vansrv7]

I have an annoying issue with category association in BO (PS 1.5.6.1)

 

When I create a product everything works as expected: i can regularly associate the product to one or more categories.

 

But if I try to edit a previously created product, in the association page the category to which the product is assigned is not checked (even if the product is correctly shown in that category in the FO) or, in case the product is associated to more than one category, there is only one category checked.

 

This causes that if I click on the "save" button, the product is removed from the category without the check symbol. So I have to remember to which category the product was associated, re-check the category and then I can save.

 

Obviously this causes a lot of problems.

 

Any solution?