I cannot find the term "banned" in any google reference so a "penalty" is the same as the "ban". A penalty does not mean that your site ranks #81479193 in the serps, it means that it's completely filtered/deindexed from the serps.
My sites that were banned disappeared completely from the index, filtered, but they were cached though. And then a day after a day got deindexed, removed permenantly, and accordingly from the cache also.
So I guess that it is strange that google updates its cache for a penalized/banned site. The same strange thing is that some googlebots still spidering the penalized sites.
I tried openning "why do googlebots spider penalized sites?" thread but it seems that moderators dissapproved it.