[juliansader]

At first glance, this drawing code might be the problem:

            reaper.JS_Composite(track_window, 
                      math.ceil(item_start * zoom_lvl) - Arr_pixel, -- X
                      item_t - y_view_start + item_bar,             -- Y
                      math.ceil(item_lenght * zoom_lvl),            -- W
                      item_h,                                       -- H
                      item_bm,                                      
                       0,                                           --x
                       0,                                           --y
                       math.ceil((item_lenght * zoom_lvl)),         --w
                       item_h)                                      --h
          end

The last --w and --h lines probably cut off part of the bitmap. To shrink and expand the ghost, the entire source bitmap must be composited, so (source w and h remain constant), and only the image size W and H in the track window changes.