I realize this is a special case, as there is really no "optimizing" going on with only one value to test, but it seems like RM should execute the process with the single value, which obviously is chosen as "optimal". Giving an error instead of a warning seems like an overreaction. Am I missing something?
no, you are absolutely right. We should change that reaction in so far that RM only yields a warning message when only one parameter value is specified. Maybe we will be able to change that behaviour already for the next release which is about to come soon.