I think one of the ideas for the foundation of C2 is that the tools be as intuitive as possible. Having things that sudden don't work isn't a good idea.
Though, one idea is to have another boolean for sprites for "Always maintain aspect ratio". But, it's easy enough to manually do that. Just like an easy way to know the individual scales is using something like what jayderyu said.
Another idea, is that whenever your set scale for a sprite, then you can have an instance variable that keeps track of that scale. Thus a comparison can easily be done with that.