See Jérôme's link.

This new German position

It aint' that new. I first noticed and reported it one month ago, but it generated scant analysis. (Regarding the 2010 bank moratorium on selling Greek debt, I first read of it in a German newspaper I bought on my travel last week.)

Regarding what this position suggests: methinks the motivation is not some big strategic consideration, but fear of the don't-spend-our-precious-tax-euros crowd in the own ranks and electorate.

preparing to bail out local institutions

Unlikely, IMHO. On one hand, as you argued, the shift from private to public hand already happened (the largest German owners of Greek debt are the EU bailout participant KfV and the publicly owned "bad bank" successor of the failed real estate bank HRE), the remaining exposure of private German banks in Greece is no more critical. In addition, the game regarding the Landesbanken (the supposedly ailing semi-public banks of federal Germany's states) is more complex: on one hand, state governments would like to keep them for financial autonomy, on the other hand, neoliberals would like to see them fail and be sold off to private banks. IOW I don't think there is a coherent strategy at work.

_{*Lunatic*, n.
One whose delusions are out of fashion.}