Signal interference and the FCC license freeze

[Rinehart]

I would like to get some information about the FCC license/CP freeze from September 1948 to April 1952. The FCC instituted it because they were unaware of the problems of signal interference when they allocated frequencies for television licenses near the end of the war.
My question is: why did they make such a mistake? One of conditions of obtaining a television broadcast license, either experimental from 1936 or commercial from 1941, was that the licensee had to have an active research program on this very subject. Did the stations provide faulty or incomplete information to the FCC, supplemented by guesses, or were there factors that they could not have anticipated at the time?
Also, since a television signal was propagated line-of-sight and its range limited by the radio horizon (10-15% farther than the optical horizon) why was there interference between stations hundreds of miles apart?