Overrides of single choice (optiongroup) question seems to work on checkbox variable level

[benzea]

It seems like the & format doesn't work there because the ID for the checkbox used during matching includes the checkbox number itself.

Now, there are different ways of solving this:

1. Drop the & thing and just use the variable _
2. Make sure the (useless) variable is not used in this case

[benzea]

The current solution is too powerful for its own good. i.e. we should only allow matching a specific box.

So, plan:

1. We can keep the &
2. Ignore the last element checkboxes in single choice mode
3. Drop the whildcard feature