I have a project named "iBook Tweaking"; I also have a project named Home with a sub-project category named for my daughter.
My Contexts categories include one named Book.
Today I clicked on "iBook Tweaking" in the projects list, to add a batch of tasks to this project. To my surprise, one of the tasks on the list was a task from my Home>Daughter project category. That task lists Book as a context.
I'm guessing that this task is being listed here because "Book" (from the category field) also appears in "iBook Tweeking" (from the project field).
The task that doesn't belong does also show up under the correct project listing.
Lorinda