Is the pin still in your adapter? Take the adapter out and shake it side to side, you should hear a rattle.
Like an HPA tank fill nipple, there is a small pin inside that gets pushed out of the way when there is input pressure, and it closes the nipple when there is back pressure. If that pin is missing or the Oring is worn out, you are just going to leak air.
You can check the Oring on the pin by simply removing the nipple from the end of your adapter.