> Error: 	"Previous cache file not found" (-1) at link
>  ...(from ...)

Humm, it appears that there is an additional case where this error can be
found: if the given file can not be found on disk, and you are updating the
mirror. In such case, an update request may be issues without actually having
the data on disk, causing troubles. (added on the TODO list)

However, I still can not reproduce the issue without having broken or deleted
files (ie. on a full mirror) ; if you have a reproducible example, please let
me know.