Everytime I use the telepprt system in Hoenn it heals my dead pokémon. All my Xatus are making me waste knock out drops, lol. Not sure if it happens in other regions too.

This was brought up and explained a couple of times in the past during Q&A-streams.
Unfortunately its a rather complicated issue because of an old script-language used in the hoenn pokecenters. From what I know trying to fix it could easily break other things, however the issue is known but there is no ETA for a fix for that as of now.

To avoid it you can simply put your Xatus in the box before teleporting.

Edited August 4, 20233 yr by Norex