Preservation of Knowledge is supposed to reduce cost of a tech by 30%.
Phalanx base cost is 50 food and 125 gold.
Once Preservation of Knowledge is researched, cost is supposed to be 35 food and 87 gold. (50 * 0.7 , 125 * 0.7)
In current build cost of Phalanx is reduced to 24 food and 61 gold.
Based on simple math, it’s most than likely that technologies moved from HoW, get the cost reduction applied twice in a row. That is easiest explanation why this happens as 50 * 0.7 * 0.7 is 24 and 125 * 0.7 * 0.7 is 61.
In other words several techs get Preservation of Knowledge bonus applied twice.
Based on short investigation I noticed that if affects at bare minimum these techs:
Phalanx - 50/125 is currently 24/61 instead of 35/87
Camel Handling - 75/200 is currently 36/97 instead of 52/140
Camel Barding - 300/700 is currently 147/343 instead of 210/490
Composite Bows - 300/700 is currently 147/343 instead of 210/490