i?m quite shure that this was working before so it might be an bug of one of the later versions.
i hadn?t set an limit at all but it OE took it like level=1 (although it was greyed out)
i got it to work like this:
enable limit, set it to 10, disable limit, |-> then i could finally increase the "skip existing files on lever higher than" option
i could get it working already. it only took some additional steps (as described above).