Yes and no I think. The way I'm interpreting it is that it does sound like a weird math bug, where the health granted per level was based on the level of the decree itself. If you had a rank 5 decree and upgraded to rank 6, the health granted on selecting that decree would be (6 * 25 = 150) instead of just +25 health.
So for example, if you had a single lvl 6 decree:
Old: 25 + 50 + 75 + 100 + 125 + 150 = 525 bonus Health
New: 25 * 6 = 150 bonus Health
So yes, a hefty nerf but definitely unintended behavior. I personally don't really mind considering the power you get from decrees is kinda insane, it was pretty normal to hit 1000 health and just one-shot everything.