Repro:
1. Pick Morphling and get Aghanim's Scepter
2. Create an allied Io and level up Tether
3. Cast Hybrid on the allied Io
4. Make the original Io and Hybrid Io cast Tether on each other
5. Make both take damage

Result: Both Ios will get immediately healed back to full hp.

Expected: Tether should not transfer health heal and mana restorement caused by Tethers.