following the info from GP4Builder's manual the shadow issue should be due to fact that *.dat, *.gp4, *.col, *track.bin are out of sync
for painting of track objects (and for some car behavior) GP4 uses the col and track.bin as a kind of quick lockup table
tracks which were updated many times over the years can have edited track objects (*.gp4) and then a *.col made from this *.gp4 (GP4Builder function) that doesn't work well with track.bin/*.dat
imho to fix the problem can be a lot of work - even with all the help GP4Builder gives there will be much tedious mouse pushing to get it all right again - drt01 did a very very good job with Spa 2011 to achieve this
a hot fix can be to build a *.col file from the *.dat of the track
as the *.dat doesn't know anything about material behavior this *.col will have no information about gravel/hard surfaces etc - you have to edit the col by hand
I've uploaded a handmade, surely not perfect *.col/track_bin combo for Melbourne 2011 by schueyfan with better car shadows - give it a try
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