The drop down feature has been raised several times. Workaround: foobar2000 + TagBox plugin. Be careful with its limitations in ID3v2 tagging, as TagBox is no longer developing. There is no problem with FLAC; i did not try the rest.
Unfortunately, the search in TagBox works for initial letters only. For full text searching you must to use other options (foobar core search, Facets, and so on).