Hello good people of FaF!
Not many people seem to know this, except for the more experienced players, but 3603 skipped out on fixing a bug.
The bug was the Seraphim ACU resto upgrade. The 2nd upgrade says that it buffs HP. Well it doesn't. The reason being is because it caused the perma-buff bug. They didn't fix it though, they just...well...removed it. I personally would love to see it back in the game without the bug part of course. Or at least the cost of the upgrade lowered to compensate for the missing feature.
Here's the other problem. If I remember correctly the buff was 10%. Nice buff and it further enhanced a units regen since its max HP was 10% more. Now that applies to all units, even experimentals <--- hence the problem.
So I consider it a bug, but it's a gray area because it does make balance changes.
My proposal, fix the bug and exclude experimental units from its affects.
If that's not possible, please fix the wording and lower the cost of the upgrade.