Odd. Here's another Hirise image of Victoria from a slightly different angle in which Sputnik doesn't appear to have the "double edge". What's more it also seems to have the classic "bowl" shape of impact crater:

Opportunity's tracks
"The thing I love about this image is the way it so vividly shows what Opportunity's been doing," Steve Squyres, said principal investigator for rover science. "You can see the tracks quite clearly that we have made as we have been traversing along the rim of Victoria Crater. The image was just recently taken by the High Resolution Imaging Science Experiment (HiRISE) camera on MRO. This is actually a subframe of a larger image, which the camera acquired on June 26, 2007. This rover first approached Victoria Crater at an alcove called Duck Bay (see tracks at left), then drove along the crater's sinuous edge in a clockwise direction before heading back. It is expected to enter the crater via Duck Bay in early July 2007. Credit: NASA / JPL / Univ.of Ariz.
http://planetary.org/image/181273main_PSP_004289_1780_sub.jpg

You may need to rotate the image to get it to show the correct relief. Then blow-up the image.

Taken from this MER update:

Mars Exploration Rovers Update:
Spirit Detours in Silica Valley, Opportunity Returns to Duck Bay to Enter Victoria.
By A.J.S. Rayl
June 30, 2007
http://planetary.org/news/2007/0630_Mars_Exploration_Rovers_Update_Spirit.html

Robert Clark