Why didn't Vladimir Arnold get the Fields Medal in 1974?

In this interview, Arnol'd says the following:

My personal relation with Pontriagin was rather good. He invited me to his house and to his seminar and showed genuine interest in my work, especially on singularity theory. This was partially due to our common interests in differential topology and control and game theory. The main reason, however, was that he wanted to say something against me at an international meeting. Pontriagin was then the Russian representative in the International Mathematical Union (IMU) and had done a lot to prevent any vote for dissident Russians. (I was blacklisted because I, along with 99 other mathematicians, had signed a letter protesting the imprisonment of a perfectly healthy Soviet mathematician in a psychiatric hospital. This was the standard method of eliminating dissidents.) The IMU had always been very political, and he succeeded.

Pontryagin wrote a book "Biography of Lev Semenovich Pontryagin, a mathematician, composed by himself". It is available online at http://www.ega-math.narod.ru/LSP/book.htm, in the original Russian. Google does a fairly good job of translation, although it refuses to translate the individual chapters completely because of their length.

In the book, Pontryagin shares a lot about the inner workings of the IMU Executive Board and his own role in holding the Soviet party line there as its vice president. For example, he recounts his version of how France got the IMU presidency in 1974, so that neither the Soviet Union nor the US would dominate.

The only relevant mention of Arnold that I could find in that book is in chapter 5. He states that in 1974 Arnold was not allowed to leave the country to lecture abroad, and that there was a conflict about this with the Executive Board of the IMU, who insisted that he should. From this, you could extrapolate the reasons for blocking Arnold's Fields medal, if the story is true.

A curious footnote to the blocking of Arnold's Fields Medal by Pontryagin (if that is what it was) is the comment Arnold made following the award of medals to three French mathematicians (mainly for work in PDE) in 1994:

Unlike the Nobel Prizes, the Fields Medals pass by many of the truly outstanding people, and in particular Russians. To give three medals at once to representatives of the French mathematical school, and all three of them noted for the art of manipulation of inequalities, is hardly a help to the international prestige of French mathematics.

This is part of an article Arnold wrote in the Mathematical Intelligencer in September 1995. It may be read here if you have the appropriate institutional affiliation.