Metadata says the video is 25i, but MPC plays it as 50i
25i and 50i are the same thing. 25i means "25 frames per second, interlaced". 50i means "50 fields per second", the latter implies interlaced video.

Likewise, 30i and 60i are the same thing. Basically, if the number before "i" is larger than 30 then it means number of fields, otherwise it is number of frames. All the existing interlaced systems I know of use 2 fields per frame. There were some systems that used 4 or even 8 fields per frame.

DVD are encoded to produce interlaced output. They also have flags that allow to save space by not repeating unneeded fields or frames. These flags are widely used in 60 Hz DVDs, I don't know how commonplace they are in 50 Hz DVDs. If the original title was a movie, you likely should treat it as 25p, not as 25i/50i or 50p.