IMHO, once one's understood the underlaying mechanisms #18 is the best solution! It is clean and effective.
I had a similar issue: trying to list custom entities, which reference multiple values from three taxonomies (i.e., each entity has 3 separate fields, and each field is set with Allowed number of values > 1 - or unlimited).
I wanted to show those linked taxonomies, as well as filtering by their label values (not simply their term-ids). Thus I had add relationships to each taxonomy... ending in i x j x k rows per each entity record - where i, j and k are the number of taxonomy terms referenced by that record (sometimes, 3 x 2 x 2, resulting in 12 rows for a single entity!).
Setting Use aggregation (in Advanced > Other) to Yes, then adjusting Group column to Entity ID in Aggregation settings for each involved field (i.e., only the fields taken from those multi-referenced taxonomy terms, no need to set this for all fields of my view) was enough to finally reduce each record to a single row.
By the way, no need to set Distinct on within the Query settings.
@hodba Thanks a lot!
You are completely right: I simply skipped to rebuild the cache.
Apologies for this silly mistake from my side.
There is no bug. Issue can be closed.