AFAICT, it works the other way round: you will see in the parent project the union(?) of the categories defined for subprojects.

IMO categorys for a project are global and categorys defined for subprojects are particular for each subproject. The hierachy should be from project to subproject. On global view for a project you could see all categorys, but , if i defined one on higher level, should be propagated to lower level.

I agree wit Paul. It makes for less clutter if each project inherits the categories of the parent. Going the other way around creates a massive mess of redundantly defined categories at the very top level.

The problem of sub-projects inheriting categories from parent projects is when a sub-project belongs to multiple project. Once a sub-project is selected as the current project, we are not aware of the parent project the user has in mind, and even if we do, we will end up with issues that were added within the context of the different parents.

The following Wiki page has the requirements for "Global Categories" and category inheritance. I've sent the review comments to the mailing list, but I will probably added it to the Wiki page as well.

http://www.mantisbt.org/wiki/doku.php/mantisbt:global_categories_requirements

This is taken core of by bug 0008435.