Follow the steps below to resync the audio and video.  Note that you need to have the Matroska tools in order to do this:

1.  Extract the DTS audio from the MKV movie using the mkvmerge GUI tool from the mkvtoolnix package.
2.  Convert the DTS to AC3 using an audio/video converter tool such as XMedia Recode, choosing Matroska Audio and selecting AC3 as the format
3.  Using the mkvmerge GUI tool, remux the AC3 audio with the original video