Not sure if this is intended but caught me off-guard.
Until recently I was on the Core plan, but now I have an Enterprise Plus one too.
I added the source for Cloud Database.
For unrelated reasons i was not able to create an new app at this time so I though to copy an app (for this db) from my Core account. It worked.
Then without adding a new source (which I should have), I copied the second app and this one worked too.
And now the surprise: my db had now the tables for both apps. So the tables for the second app were created in my postgresql db for the 1st app.
This can be a real bugger; how am I going to copy an app on this account without getting one of my existing DBs becoming a “host”?
This is a kind of normal behavior when you copy an app and you select the database as a source. If you don’t want to do that, you need to remove the option “Make a copy of the data for the new app”. When this option is set as OFF, the new app starts to use the same source that belongs to your original app.