Unexpected result with apoc.text.sorensenDiceSimilarity

A bit confused in regards to string similarity using Sorensen-Dice. Apparently it makes a difference in what order parameters are being passed.

apoc.text.sorensenDiceSimilarity("+46xxxxx2260", "+46xxxxx2226") as score1,
apoc.text.sorensenDiceSimilarity("+46xxxxx2226", "+46xxxxx2260") as score2
score1, score2

One of these "scores" (similarity coefficients) will say 1.0, the other 0.909090...

Does not make sense to me, but perhaps there's something with the algorithm I'm not aware of? Any insight is appreciated.

P.S. "Neo4j Kernel", "3.5.9", "community"