Thanks for the clarification. But since blockchain.info is connected to lots of nodes, let's say I run node A, that connects only to node B. I restrict node A to a single connection. Whenever I send a transaction, then this transaction goes through B, that further propagates it on the network. If blockchain.info has a connection to node B, then node B will be listed as "relayed by ip" at blockchain, right?
Yes, if it is blockchain receives the transaction from it before anyone else.
I'm not sure if the ip of A is automatically logged at node B when issuing the tx, but at least the ip of A will not be shown on blockchain.info. In the event someone looks at the debug.log of node B, they might however see that the transaction came from node A.
Some person might then misinterpret "relayed by ip" as having a direct association with the tx in question, and thus try to get answers from the entity behind that ip. That was my point.
I don't think that bitcoin core will log which ip it receives a transaction from, but a custom client can be written to do so.