BNP Paribas issued a report named “The Bundesbank’s Bond Purchases in 1975”. The Bundesbank bought some German financial assets, among them German sovereign bonds. Here is the essence:
The Bundesbank has raised objections to the ECB’s potential sovereign bond purchases.
However, back in 1975, when private demand for long-term bonds plunged, the Bundesbank bought post, telecom and sovereign bondsworth around 1% of GDP.
The original numbers come from the Geschaeftsbericht of Deutsche Bank, which apparently changed the url of the file in the meantime. However, it is still online at the same site. You can download it here (in German).
Disclaimer: I don’t know whether they “did it” in summer. It just made a nice title.