Are you sure that this is a bug? Can you give us steps to reproduce consistently?
Does this always happen or only when these artists are playing? The only way I could reproduce something similar was to play some pretty obscure music which, with the settings you have in the auto DJ configuration, results in a very small pool of tracks to select from in my library (and therefore produces repeat selections).
Perhaps try reducing the Last FM % similarity setting (which may increase the possible matches - I am not sure)
Also, to prevent repeats you could try reducing the number of tracks in the initial list and upcoming settings, along with applying a custom filter with a rule <Last Played> is not in the last 2hrs (or something similar).
And, maybe more out of curiosity, I see that you have 'Selection Mode: random - select by' set to <Album + Genre>. I assume this is a virtual tag - could you detail the formula for this tag.