Merge declined

I stumbled upon a TV movie entry for "Polizeiruf 110: Aquarius" under https://www.imdb.com/title/tt37813541/reference/.

However, this is actually an episode of a series and already has an entry under https://www.imdb.com/title/tt1542295/reference. I submitted a merge (#251125-221346-996000), but it got declined. Did I do something wrong or is this a processing error? I'll note this is one of several episodes of the show to have an additional TV movie entry: https://www.imdb.com/find/?q=polizeiruf%20110&ref_=ttrv_nv_srb_sm. But I want to clear up this situation first before submitting any additional corrections.