Just as the title says.
I went and tested my new and shiny 3-hour HP buff tonight, only to find out that it's bugged and instead of applying a 25% total max HP modifier, it adds a flat 25% to whatever your mods already added to your warframe's base.
This means that in case of a simple maxed bronze-ranked Vitality (440%) we're getting ~5.6% more health, and in case of a full Umbra setup (770%) the True Master bonus amounts to a "whooping" 3.2% more HP.
I refuse to believe this insult of a buff was intended. Please tell me it's a bug. Pretty please.