Occasionally, when I begin to do a next action I discover that it wasn't THE next action after all, but it still is a future action. Home projects frequently throw these curves at me--I get started on doing a next action and SURPRISE! I find a hidden problem that I don't have the means to deal with at that moment, I discover that I don't have enough screws, or I need to buy a special tool. So what do I do now?
First, I change the category of the original action to "unfiled" or "none". This removes it from the context list but keeps it in the task list application so that I can reinstate it easily. Second, I identify the true next action and park the reminder in the appropriate place. When I'm able to do the original action, I change its category so it appears in the appropriate context.
I only use the "unfiled" category as a short-term holding area for definite future next actions that I added to my context lists at the wrong time. Therefore it is a VERY short list. I don't put planned future actions there--those go in my project support material. During the weekly review, I prune this list just as I do my other lists.
It's worked really well for me so far.