[DCP-o-matic] 2*MKV, A/V from one, subs from the other...?

Hi, Having two MKV files each containing audio, video and subtitles... Would it possible using DoM to make a DCP containing audio and video track from the first MKV and the subtitle track from the other? I have tried to use the Timeline functionality (DoM 2.5.0) but when I try to remove the tracks not needed (audio and video from the second MKV) all tracks of that MKV is removed. Is this a bug, or am I doing it the wrong way? Cheers, Christian