fixed support of multiple objects for same predicate

similar issue that we had in #19 then fixed in #21 

i stumbled on this bug while working on support for multiple languages for http://unmonastery.net , made not the cleanest fix i can imagine but it works and all tests pass!

at some point :calendar: i'll need to do refactoring round to tidy up few things... especially tests

@mcollina if you feel ok with merging it maybe you could release it right away as 0.3.1 ?