Denied

Last week, on August 20, the President of Hungary, Sólyom László was refused entry into Slovakia.
The president was going on a private visit to a town in southern Slovakia with a majority ethnic Hungarian population to unveil a statue of St. Stephen, the first king of Hungary.
The reason the Slovak government gave for refusing entry to the Hungarian president was the day he chose to come on. The Slovak government told Sólyom László that he could come on any other day, just not August 20th. When he came anyway, he was turned away at the bridge where he tried to cross into Slovakia.
This is the complication - because whereas for Hungarians August 20th is Saint Stephen's day - one of their most important holidays, when they remember the founding of the Hungarian kingdom, which used to include the territory of modern Slovakia and Transylvania - in Slovakia August 20th is the anniversary of the Soviet-led invasion of Czechoslovakia in 1968, in which the Hungarian army also invaded Czechoslovakia to shut down the "Prague Spring" - an attempt by Czechoslovakia to move away from communism and Soviet domination.
The problem is that Hungary and Slovakia are both EU members, and Slovakia's denial of entry to the Hungarian president is contrary to EU law which permits freedom of movement between countries.
This isn't even the first time this kind of thing has happened to Sólyom László. On March 15, he went to Romania, to celebrate Hungary's national day with Transylvanian Hungarians, and while his plane was in the air, he was refused landing permission, and ended up having to come into Transylvania by car. Pretty embarrassing for a president...
Both Romania and Slovakia are sensitive to Hungarian territorial claims to their land, and view moves like these by the president as challenging their territorial sovereignty.
I can personally understand why Slovakia and Romania are concerned about Hungarian claims to their land. I can also understand the Hungarians, who don't want to lose touch with fellow Hungarians who were separated from Hungary not by their own choice.

What do you think? Was Slovakia justified in doing this? Is the president of Hungary challenging the sovereignty of these nations by his visits there?