An alternative viewpoint: you haven't properly defined your contexts, or have assigned the wrong one to the task. If you have tasks that can only be done at some supermarkets, either your supermarket context shouldn't be so inclusive, or you should have a context for gourmet supermarkets, or bargain priced supermarkets, or whatever the distinction is that makes one suitable and another not. i find the hierarchical context support useful for this. I've got an Errands context tree that among other things, has a nested Grocery store context. Items that can reasonably be bought at any grocery store I might encounter will go in the Errands : Grocery store context. Underneath, I've got nested contexts for specific stores that I patronize where I file actions that should be done at a specific store (or class of stores) -- if someone has chicken on sale this week, I'll put the "buy chicken" action in the more specific context for that store. When I go to one of the specific contexts, I'll get whatever is listed in its context, of course, but I'll also check the parent context to see if there is anything on the general list that I can get while I'm there.
Remember, a context specifies a tool or location or person or other such constraint needed to do a task. You shouldn't have to look at a list of tasks for a given context and re-evaluate whether or not you can actually do that task (at least from the standpoint of being in the context) or you lose most of the value of the concept. As an example, having a Computer context would not be good if half of your computer-related tasks have to be done with Windows and half with Mac OS X -- you'd be constantly scanning the list, wasting energy and concentration skipping the items you couldn't do at the computer you were using.
I'm not saying that it wouldn't be an improvement for the maps display to offer the option of showing more choices. My argument holds whether it shows one choice or many -- if your context shows an action that you can't do while in the context, you've misfiled the action or the context definition needs refinement.