Rasterize a graphic with Background None gives unexpected result using GradientFilling

I would like to combine several images with ImageCompose using Images and rasterized graphics.
When I create a Disk with RadialGradientFilling and want to have no background on the rasterized graphic it gives an for me at least unexpected result.

Rasterize(
 Graphics({{RadialGradientFilling({0, 1} -> {RGBColor(
       0.7803921568627451, 0.9084967320261438, 1.), RGBColor(
       0.011764705882352941`, 0.5882352941176471, 1.)}), 
    Disk({3, 5}, 1)}}, PlotRange -> {{0, 10}, {0, 10}}, 
  ImageSize -> 300), ImageResolution -> 72)

gives (without Background->None)

enter image description here

and using Background -> None

Rasterize(
 Graphics({{RadialGradientFilling({0, 1} -> {RGBColor(
       0.7803921568627451, 0.9084967320261438, 1.), RGBColor(
       0.011764705882352941`, 0.5882352941176471, 1.)}), 
    Disk({3, 5}, 1)}}, PlotRange -> {{0, 10}, {0, 10}}, 
  ImageSize -> 300), Background -> None, ImageResolution -> 72)

gives

enter image description here