Unsealed Spellbook rune interaction (exploit?) for full flash cooldown reset. Is this OK?

Apparently with two shards, flash on cooldown and your other summoner spell not on cooldown you can instantly refresh flash by doing the following:

Trade the "on cooldown" flash with another summoner spell which will inherit the remaining cd

Trade your other summoner spell thats not on cd with flash and flash will now be completely off cd and available

This technically makes sense, but it came off as some what confusing at first.

I feel flash should simply be made unavailable until it finishes it's original cooldown, even if you intend swap to it out with another spell.

What do you guys think?