instead of getting a +50% buff, when applied it only shows approximately a +30 increase--why??

It's not a bug. Moved to Game Discussion. 

How do speed bonuses work?

 Let's imagine 1 builder can build a house in 1 day (or 24 hours).

Earlier our Bonuses were cutting the construction time. Let's say the bonus is 50%. In that case 1 builder will build 1 house in 12 hours (50% less).

But a few months ago we have changed the way your bonuses are applied. Now they rise speed instead of cutting the time.

How does it work?

Let's imagine that our builder started working 50% faster.

It means that 1 builder will build 1,5 houses in 1 day (24 hours), or 1 house in 16 hours. Not 12 like it would be if the Bonus cut the building time for a house.

The same formula is behind all construction/training/etc. bonuses.