ZSE Controller described an airspace incursion event when ERAM automated software failed to Auto-Hand Off traffic to S46.

Narrative

An E190 entered Seattle Approach (S46) airspace without a hand off. He was issued a clearance to descend via the GLASR7 arrival landing north; which requires him to cross JAKSN AOA 160; then descend to 120. S46 owns 150 and below. Communications were transferred outside S46 airspace without me noticing that the CID did not have an R in front of it and therefore the RADAR hand off had not yet occurred. I noticed the situation when the aircraft was at FL133; inside Seattle Approach; and called them to verify they had RADAR Contact; which they confirmed. I would recommend some changes to the ERAM auto-hand off system. This occurred during a live ERAM run to a problem that has been known since our first run. Standard procedure at ZSE is that aircraft come to the A Area at altitude with PD to 240; using an interim altitude in the data block (i.e. 240T360). When the crossing or descend via clearance is given to go on the STAR into Seattle Approach; most R-Sides put an interim altitude of 120 (i.e. 120T360). We have noticed that when the interim altitude is on; the data block will not auto hand off to Approach; so I use the work around of using only hard altitudes in ERAM. This is an ERAM safety issue which I believe should be addressed and fixed.