Establishing a Sanctuary in a system adjacent to another faction leads to an immediate outpost removal demand. It doesnt matter if the sanctuary was made by system hack or successful invasion. The diplomatic pressure does change based on acceptance/refusal, but agreeing to remove the 'outpost' doesnt remove the sanctuaries. This applies to any normal faction.

Military Example Save Complete the invasion (Blitz) on the Nakalim, and you will find the Sophons to the north instantly know what youve done. However, the system does not say the Sophons detected it.

Edit: this bug is with the opt-in patch preview version