ZOA Controller described an apparent false conflict alarm when an Airline Data Block failed to drop off the operational display after the aircraft had landed; the reporter listing Data Link/ATOP anomalies as causal factors.

Narrative

While working Oceanic Sector 3 I cleared Air Carrier Y for arrival KWA Island Airport. After arrival; I received arrival report from KWA Base Operations. Opened appropriate window; hit modify and entered arrival time. FPEA was opened for Air Carrier X. ATOPS automatically deleted Flight Plan for Air Carrier X. I was distracted by flashing orange conflict and other operations. I did not perceive disappearance of Air Carrier X Data Block. Approximately five minutes later saw Air Carrier Y Data Block still on scope. [I] re-entered arrival message using same process. This time Air Carrier Y disappeared from scope as expected. Air Carrier X was Data Linked aircraft. Normal expectation is that Air Carrier X would have to be logged off Data Link prior to ATOP allowing controller to delete flight plan information. Recommend that arrival airport should be a necessary entry into FPEA window to report arrival for aircraft. System should do a logic check on arrival airport. Data Link aircraft should not be deleted out of ATOP until logged off Data Link.