As described on the mailing list .
Consider this example synonym set [bier,brouw] where bier means beer and brouw is the stemmed version of brouwsel (brewage, concoction), and consider these parameters on /select:
The queries q=bier and q=brouw both give the desired results. However, for q=brouwsel something (partially) unexpected happens:
This results in a BooleanQuery where, due to mm=2, both clauses need to match, giving very few matches. Removing KeywordRepeat or setting mm=1 of course fixes the problem, but that is not what we want.
Will shortly attatch a patch containing a unit test proving the problem is real.