1. User searches for "stocks oil gold" with MM set to "50%"
2. User adds "-stockings" to the query: "stocks oil gold -stockings"
3. User gets no hits since MM was ignored and all terms where AND-ed together
The behavior seems to be intentional, although the reason why is never explained:
// For correct lucene queries, turn off mm processing if there
// were explicit operators (except for AND).
boolean doMinMatched = (numOR + numNOT + numPluses + numMinuses) == 0;
(lines 232-234 taken from tags/lucene_solr_3_3/solr/src/java/org/apache/solr/search/ExtendedDismaxQParserPlugin.java)
This makes edismax unsuitable as an replacement to dismax; mm is one of the primary features of dismax.