"Libertarian" parties are often fronts for right-wing nationalists. See for example the great proportion of neo-Confederate Paul supporters.
The FDP didn't have a "Libertarian" platform back then. It had a Liberal (and thus sort of Libertarian) minority wing and a Nationalist majority wing.
Yeah but the communists also haven't gone Hungary 1956 yet. Also KPD is more interesting for alternate history story reasons than SPD.
The relevant German issue equivalent (as far as 'soft' Commie support goes) is the Berlin Blockade. The 1949 election was after the Berlin blockade. Hence (rl) results well below those of the first round of state elections and the first two rounds of local elections (most states held new local elections in 1948.) However the effect hadn't fully set in - from 1950 on the KPD polled even lower - but fell only very slowly after 1950, the remaining 3% being hard to crack (the party was banned after 1956, but front organizations stood in most elections until the official founding of the DKP.)