why ffmpeg changes video stream from interlaced to progressive when it is set to copy the the stream
Looks like it is a FFmpeg bug.

I tested to remux an AVI with DV to AVI with latest FFmpeg, and the resulting "video properties" chunk indicates progressive, even if the source AVI has the right "video properties" chunk:

010F4   Video properties (76 bytes)
010F4    Header (8 bytes)
010F4     Name:                               vprp
010F8     Size:                               68 (0x00000044)
010FC    VideoFormatToken:                    0 (0x00000000)
01100    VideoStandard:                       0 (0x00000000)
01104    VerticalRefreshRate:                 50 (0x00000032)
01108    HTotalInT:                           720 (0x000002D0)
0110C    VTotalInLines:                       576 (0x00000240)
01110    FrameAspectRatio Height:             3 (0x0003)
01112    FrameAspectRatio Width:              4 (0x0004)
01114    FrameWidthInPixels:                  720 (0x000002D0)
01118    FrameHeightInLines:                  576 (0x00000240)
0111C    FieldPerFrame:                       1 (0x00000001)
01120    Field (32 bytes)
01120     CompressedBMHeight:                 576 (0x00000240)
01124     CompressedBMWidth:                  720 (0x000002D0)
01128     ValidBMHeight:                      576 (0x00000240)
0112C     ValidBMWidth:                       720 (0x000002D0)
01130     ValidBMXOffset:                     0 (0x00000000)
01134     ValidBMYOffset:                     0 (0x00000000)
01138     VideoXOffsetInT:                    0 (0x00000000)
0113C     VideoYValidStartLine:               0 (0x00000000)


It should be 

010F4   Video properties (108 bytes)
010F4    Header (8 bytes)
010F4     Name:                               vprp
010F8     Size:                               100 (0x00000064)
010FC    VideoFormatToken:                    0 (0x00000000)
01100    VideoStandard:                       0 (0x00000000)
01104    VerticalRefreshRate:                 50 (0x00000032)
01108    HTotalInT:                           720 (0x000002D0)
0110C    VTotalInLines:                       576 (0x00000240)
01110    FrameAspectRatio Height:             3 (0x0003)
01112    FrameAspectRatio Width:              4 (0x0004)
01114    FrameWidthInPixels:                  720 (0x000002D0)
01118    FrameHeightInLines:                  576 (0x00000240)
0111C    FieldPerFrame:                       2 (0x00000002)
01120    Field (32 bytes)
01120     CompressedBMHeight:                 288 (0x00000120)
01124     CompressedBMWidth:                  720 (0x000002D0)
01128     ValidBMHeight:                      288 (0x00000120)
0112C     ValidBMWidth:                       720 (0x000002D0)
01130     ValidBMXOffset:                     0 (0x00000000)
01134     ValidBMYOffset:                     0 (0x00000000)
01138     VideoXOffsetInT:                    0 (0x00000000)
0113C     VideoYValidStartLine:               1 (0x00000001)
01140    Field (32 bytes)
01140     CompressedBMHeight:                 288 (0x00000120)
01144     CompressedBMWidth:                  720 (0x000002D0)
01148     ValidBMHeight:                      288 (0x00000120)
0114C     ValidBMWidth:                       720 (0x000002D0)
01150     ValidBMXOffset:                     0 (0x00000000)
01154     ValidBMYOffset:                     0 (0x00000000)
01158     VideoXOffsetInT:                    0 (0x00000000)
0115C     VideoYValidStartLine:               0 (0x00000000)


I have open a bug ticket at FFmpeg tracker with an example about how to reproduce the issue.

Note that the DV stream is correctly remuxed only (it is still interlaced, no conversion), the issue is only a piece of metadata in the created AVI file, reason you see both "progressive" (from AVI) and "interlaced" (from DV) in the MediaInfo output.

Jérôme, main developer of MediaInfo.