sorry maru...
might be a bit of confusion when writing it in a hurry.
I thought, that autosave does indeed just delete the number of files with the same file-name, instead of deleting all autosaved files. I had rendered 3 diferent cameras and set the number of images kept on render end to "2"... so i actually lost the first rendered one.
I believed that when autonaming the filenames by current camera name "%v" i could prevent the autosave-feature deleting the previous rendered versions.
But now i know - maybe its misleading, that i put it into bug/feature thread. although it be great to have it as a feature, not deleting different names.