Mearis

A priest at arena junkies checked a bunch of coefficients, and the way several multipliers interact is currently bugged:

ROFL At Blizzard! - Arena Junkies Forums

In particular, improved PW: S is currently absolutely crap and not worth tanking as a talent.

<manly> then my sister calls and proposes the one thing that has never before occured in my entire life

 

bbartlog

Interesting information. To summarize

- Renew has a minor bug that makes it heal for very slightly less than it should (if talented)
- Prayer of Mending has a bug that makes it heal for quite a bit more than it should (if talented)
- Improved PW:S has a bug where the percentage bonus is applied based on the base amount (not the total)

Details at the link. His formulas are wrong as written - he consistently writes things like

1.05*(1.05+1.10)*1.10 when what he means is
1.05*(1.05+0.10)*1.10

...but if you're familiar with the general issues he's discussing you will know what he means.

 

Althor

I noticed during testing of the Shadow talents in beta that the following effects all stack additively:
Twin Disciplines
Improved Shadow Word: Pain
Darkness

Shadowform and Shadowweaving are still applied multiplicatively.

Misery multiplies just the spellpower amount.

Mana cost reduction talents also appear to stack additively and they round down to an integer mana cost.

 

aurelito

I just did a quick test with 1109 spell power, the absorbed value was 4892.

The expected value is:

(2230 * 1.15 + (1.5 / 3.5 * 1.88 + 0.4) * 1109) * 1.15 * 1.04 * 1.05 = 4899.

So I'm afraid I can't confirm the PW:S scaling bug. Maybe he was extrapolating from the glyph value? I know for sure that the glyph ignores the 15% scaling.