I've been having problems with Oceanic not "releasing" me back to Center at the end of Oceanic segments. For instance, today on a flight from TJSJ to KTPA, I set the Oceanic sector as follows:
SAPPO being the end of the ACONY3 SID and beginning of Oceanic airspace and RUTOC being the last waypoint prior to reaching the end of Oceanic airspace (as best approximated by Navigraph).
In reality, as the logs should bear out, I wasn't released from Oceanic until passing below 11000 around COSAR/DSIDE, well into the BLFRG2 STAR and less than 10 minutes from landing.
This seems to happen to me quite frequently, so I usually just skip using this feature. It always initiates at the right time, just more often than not I'm left to "aviate and navigate" to force the "communicate" that I want.