ZSE Controller voiced concern regarding ERAM deficiencies that resulted in incorrect aircraft data block correlations.

Narrative

A B737 departed KPAE; which is presently worked by ZSE. Immediately after departure; the aircraft was handed off to S46; then about 10-15 miles later; handed back off to ZSE. I was working that second ZSE sector; where I took the aircraft that should be climbing to 150 from S46 and climbed it to altitude. When the hand off flashed; I accepted the hand off. The Data Block then immediately went into Coast Track and the target that was formerly associated with it kept moving along the assigned route but it was tagged up as a different aircraft. Apparently during departure the B737 cycled through Transponder codes and ERAM associated the other aircraft's Data Block with the B737; even though that other aircraft had already been worked by ZSE and handed off to Whidbey Approach and the B737 corrected his squawk after only 2 hits. The actual event was just confusion as I struggled to unpair the Data Block and re-pair it correctly. I had to have the B737 IDENT to verify he was the target in question and it caused a delay in his climb as the situation was figured out. This process was time consuming and frustrating and luckily happened at a low volume time; otherwise it would have been quite an issue during a busy time. This was caused by ERAM incorrectly pairing a target and then not being easy to unpair; even when an incorrect Data Block is obviously paired. Recommendation; I recommend discontinuing the use of ERAM until its many issues are fixed and falling back to HOST.