Muxing interlaced video

[kingcrimsonster]

Source file options:
Format : MPEG Video
Frame rate : 25.000 FPS
Standard : PAL

Output File Options:
Frame rate mode : Variable
Frame rate : 50.000 FPS
Original frame rate : 25.000 FPS

Where do these values come from?

for the video no indication of VFR.

Cu Selur

the sorce file has a constant frame rate. It's right.
When I mux this file in the *.mkv with Mkvtoolnix output file has a constant frame rate. It's right.
When I mux this file in the *.mkv with Hybrid output file indicated as vfr. It's wrong!