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 (also check it out here for free access).