metadata API returns different doi than queried and very incomplete record

[timwoelfle]

Dear OpenCitations, first of all thanks for your wonderful work! I'm not sure if this is the best place where to put this, but I haven't found a better place.

I've noticed weird behavior by the metadata API on this call:
http://opencitations.net/index/api/v1/metadata/10.1080/00031305.2018.1543137

It returns a different DOI (seems to of a preprint) than the called for (10.1080/00031305.2018.1543137). Also the record is very incomplete, missing everything but the fields "reference" and "citation" (I haven't checked their correctness).