Are you sure it's 50i?!? Panasonic cameras can play "tricks" in AVCHD by duplicating frames ...
I get the exact same problem with AVCHDlite's fake 50p
The only way I get a duplicate of the exact stream is to use DSS2 (DirectShowSource2 from a Haali Splitter install directory, it reports the 50 fps right, and it also shows the duplicate frames) ...
FFMpegSource2 only shows 25fps, DGTools (DGAVCIndex, DGAVCIndexNV, DGTools) reports 50fps but only shows the moving frames (not the duplicate statics, no matter what it's indexed with, no matter if the "honor pulldown" flag is set or not!), DirectShowSource isn't frame accurate (so any non linear functions tend to produce jumpy frames) ...
Example clips that stuff all these filters up (MTS file with AVC video and AC3 audio, straight from a Panasonic AVCHDlite device):
00000.MTS,
00001.MTS,
00002.MTS
For now, I am using DSS2() if I need a duplicate of the stream transcoded or processed, but even DSS2 is reporting too many frames in the stream (so it can crash at the end of an encode unless I also use Trim(0,reported frames - 4), if I am manipulating the stream I will use FFmpegSource2 + AssumeFPS(25) + MSU_FRC(2) ...
They are funny streams, no doubt, because if you play the streams you will notice frame 0, and frame 1 are actually different images, then frame 2 is a duplicate of frame 1, then frame 3 is different again with that pattern repeated throughout ...
7ek