a big difference between the source and target

[Selur]

With Colormatrix enabled ent set to 'Rec.709'->'Rec.601' the preview script is:

SetMemoryMax(768)
SetMTMode(2,16) # changing MT mode
LoadPlugin("G:\Hybrid\AVISYN~1\DGDecode.dll")
LoadPlugin("G:\Hybrid\AVISYN~1\ColorMatrix.dll")
# loading source: F:\TestClips&Co\MPEG-2\Tablitsa_colormatrix.mpg
#  input luminance scale tv
Source = MPEG2Source(d2v="H:\Temp\mpg_e0b8c6319ad8a0dd51e4cdd1d25dd581_4827.d2v",info=3)
# current resolution: 720x576
SourceFiltered = Source
# color modifications
SourceFiltered = SourceFiltered.ColorMatrix(mode="Rec.709->Rec.601",interlaced=true,hints=true)
# filtering
# adjust color to(2): RGB32
SourceFiltered = SourceFiltered.ConvertToRGB32(matrix="Rec601")
Source = Source.ConvertToRGB32(matrix="Rec709")
StackHorizontal(Source, SourceFiltered)
return last

disabling the option and the preview script is:

SetMemoryMax(768)
SetMTMode(2,16) # changing MT mode
LoadPlugin("G:\Hybrid\AVISYN~1\DGDecode.dll")
# loading source: F:\TestClips&Co\MPEG-2\Tablitsa_colormatrix.mpg
#  input luminance scale tv
Source = MPEG2Source(d2v="H:\Temp\mpg_e0b8c6319ad8a0dd51e4cdd1d25dd581_4827.d2v")
# current resolution: 720x576
SourceFiltered = Source
# filtering
# adjust color to(2): RGB32
SourceFiltered = SourceFiltered.ConvertToRGB32(matrix="Rec709")
Source = Source.ConvertToRGB32(matrix="Rec709")
StackHorizontal(Source, SourceFiltered)
return last

I also see a clear color switch when en- and disabling the option while having the Avisynth Filter Preview open.
-> can't reproduce the issue you describe.

Cu Selur

Ps.: Preview script is inside the temp-folder (while Avisynth Preview is used) if you want to check yourself.