Convert BluRay to MKV with MKVmerge no FPS set

[whachano]

I am converting a BluRay to MKV - 1:1 conversion in terms of size. The movie is 23.976 fps.
But after running MKVmerge, there mkv file has no FPS and cant play.

Using TSmuxer to demux .264 video stream
Then running the .264 file through MKVmerge. MKVmerge tells me it cannot determine the FPS.
I go to format specific options and choose 24000/1001

BUT the resulting MKV has no FPS and cannot play. Why?