Major Description
When sow=false, the edismax query parser creates dismax-per-field queries when field analysis is different enough that query structures differ per field (stopwords in one field only, e.g.). (By contrast, dismax-per-term queries are produced when sow=true or when query structures are the same across all fields.)
However, the code to determine whether per-field query structures differed wasn't aware of boost queries. As a result, when sow=false and boost are specified for at least one field (e.g. q={!edismax sow=false}text&qf=fieldA^2+fieldB^4), dismax-per-field queries are always produced, even when per-field query structures are equivalent.