I don't know if this is a bug or intentional; but it is definitley irritating.  I am curious as to why it takes 20 material before one can initiate the construction of one's first Pioneer Unit.  It appears as if you have to create 4 to start; but when you finally acquire the 20 material and click to create those four it switches to one and only requires 5 material.

SK

PS.  In addition, once I get to the point where the Pioneer unit only costs 5 material/1 person, I am able to load a save from any previous turn and the cost is only 5 material/1 person.

PPS. The problem appears to be connected to the Quantity Icons one uses for producing Peasants.  There are two icons: the first one looks like a single character, but if one hovers over it the word "Party" appears and clicking on it causes the quantity to switch to four units; the second icon appears as three units and clicking on it causes the quantity to switch to eight units; there is no switching back to a single unit.  In addition, once either of the icons is clicked and then one switches to selecting a Pioneer the cost is 20 material and 4 people.