Scratch that Causative Alternating Itch

The other day I overheard the following dialogue:

A: Look at all these bug bites.
B: Wow. And you haven't been itching them?
A: No, I haven't been scratching them.
B: That's what I meant. Are you saying there's a difference between itch and scratch?
A: [Some description of how itch is a sensation and scratch is an action]
B: Huh. I never noticed a difference.

Let me first posit that B does indeed treat them differently and would never say "These bug bites really scratch!". But A is objecting to B's use of the verb itch as a transative verb synonymous with scratch, not the other way around. The truth is, I think it is very common that itch be used in this way, and the dictionaries I checked agree.

But what is most interesting to me is the question of how itch relates to other verbs that have in/transitive alternation. The examples are boundless, but I think tickle and hurt are most appropriate. Consider the sentence

It Vs when you V me.

and replace V with tickle, hurt, burn, or sting. These are examples of causative alternating verbs, which can both represent a state, and the action which causes the state. Itch is somehow different. It works if you plug it into the sentence, at least grammatically, but begs the question, what action causes someone to itch? It is also clear that this causative use of itch is distinct from its use as a synonym for scratch.

But I have at least one crazy theory. Unlike the other verbs of sensation, itch seems to be as much a desire for a certain action (scratching) as it is a specific sensation. In other words, itch can be interpereted as meaning cause to [want to] scratch, which is already a causative. This would explain why plugging it in for V is a bit strange. But if itch is already causative, then could it have causative alternation? Then can we extrapolate a more basic meaning? Of course, and that meaning is none other than scratch. This is my explanation for why itch has acquired the meaning of scratch.