I created an icon file (.ico) with Axialis IconWorkshop v6.70, containing several icons ranging from 256x256 down to 16x16. For the 256x256 I used a drawing that I copied/pasted from a drawing program. It shows correctly both in the edit window and the thumbnail/icon. The other resolution icons were automagically created from the large one by IconWorkshop. But when I close and reopen the file all resolutions are OK, except the 256x256, which appears as a black square:
Is there anything that I missed?
After karel's comment I tried importing a .png image instead of the copy/paste, but the result is the same.