Hopefully Steven can explain why that setting might be causing a problem, then.
@Steven, I can confirm this issue. If I turn on the similar artists feature, I get artists starting with: G, I, L, A, C, A, B, C, A, A, A, N, D, A, B, B, A. If I turn it off, I get: A, J, D, P, M, M, E, D, A, S, F, D, M, A, T, R, B, E, D.