The 1852 Congressional act, “An Act to make Land Warrants assignable, and for other Purposes,” (Thirty-Second Congress, Session 1, Chapter 19, 1852) stipulated that if military land warrants were used to locate (ie. purchase) federal land whose value was more than $1.25 per acre, the individual using the warrant to locate the land had to pay the difference.

Add that to the list of things of which I was not aware.

A PDF of the 1852 Act is available online.